No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Mechanisms of Blood Flow Restriction: The New Testament
Abstract
When restricting blood flow for the purpose of increasing or maintaining muscle fitness, the aim is to reduce the amount of arterial flow into the limb and restrict the venous flow out of the limb. Doing so has been shown to elicit positive adaptations with regards to skeletal muscle size, and strength, while some evidence also eludes to beneficial effects on vascular and bone tissue. Regarding skeletal muscle, the main benefits of blood flow restriction are the ability to stimulate increases in size and strength while avoiding the greater mechanical stress associated with traditional high-load resistance training, and the greater volumes required when exercising with low loads to failure. While the most robust benefits are observed following blood flow restriction during low-load resistance training, evidence suggests positive adaptations occur while restricting blood flow during low-intensity aerobic exercise, and perhaps even during periods of disuse in the absence of exercise. Although the exact mechanisms are unclear, most of the evidence seems to allude to cell swelling and metabolite-induced fatigue during exercise stimulating synthetic pathways that can lead to muscle growth. While the blood flow restriction stimulus has been shown to be relatively safe for participants, the practitioner should be cognizant of the relative pressure being applied to the underlying tissue. This is important as cuff type, cuff width, and limb circumference can all influence the restrictive stimulus. Therefore, to ensure a similar, safe stimulus all variables should be accounted for.
... They are believed to induce earlier, peripherally mediated fatigue, resulting in greater motor unit recruitment, as suggested by the fact that BFR under low loads has similar recruitment to that of high load resistance training. 7,14,15 In addition, type II fast-twitch muscle fibers, which are normally only preferentially recruited at greater intensity, are activated at lower loads under BFR conditions, providing rationale for the increased muscle hypertrophy in low-load BFR in comparison with similar lowload exercise alone. [16][17][18] However, greater motor unit recruitment is not limited to muscles distal to the area of occlusion. ...
... In the interest of providing concise, practical recommendations for producing muscle hypertrophy with BFR-RE, 20% to 40% of 1 repetition maximums are recommended in concert with BFR cuff pressures set between 40% and 80% of limb occlusion pressure (LOP). 35 Four sets of repetitions (30,15,15,15) has been most commonly used in practice and produces the beneficial adaptions noted in BFR. Generally, rest between sets of 30 to 60 seconds is recommended, with concern that longer periods and intermittent BFR (relieving the cuff pressure between sets) may limit the stress for adaption. ...
... In the interest of providing concise, practical recommendations for producing muscle hypertrophy with BFR-RE, 20% to 40% of 1 repetition maximums are recommended in concert with BFR cuff pressures set between 40% and 80% of limb occlusion pressure (LOP). 35 Four sets of repetitions (30,15,15,15) has been most commonly used in practice and produces the beneficial adaptions noted in BFR. Generally, rest between sets of 30 to 60 seconds is recommended, with concern that longer periods and intermittent BFR (relieving the cuff pressure between sets) may limit the stress for adaption. ...
Blood flow restriction (BFR) is an expanding rehabilitation modality that uses a tourniquet to reduce arterial inflow and occlude venous outflow in the setting of resistance training or exercise. Initially, this technique was seen as a way to stimulate muscular development, but improved understanding of its physiologic benefits and mechanism of action has allowed for innovative clinical applications. BFR represents a way to decrease stress placed on the joints without compromising improvements in strength, whereas for postoperative, injured, or load-compromised individuals BFR represents a way to accelerate recovery and prevent atrophy. There is also growing evidence to suggest that it augments cardiovascular fitness and attenuates pain. The purpose of this review is to highlight the physiology and evidence behind the various applications of BFR, with a focus on postoperative rehabilitation. While much remains to be learned, it is clear that blood flow restriction therapy stimulates muscle hypertrophy via a synergistic response to metabolic stress and mechanical tension, with supplemental benefits on cardiovascular fitness and pain. New forms of BFR and expanding applications in postoperative patients and athletes hold promise for expedited recovery. Continued adherence to rehabilitation guidelines and exploration of BFRs physiology and various applications will help optimize its effect and prescription.
Level of Evidence
V, expert opinion.
... Nevertheless, these findings provide significant benefit following hip arthroscopy and anterior cruciate ligament reconstruction, where proximal musculature strengthening, and control are key for successful postoperative outcomes [75,76]. Additionally, following independent, unilateral upper-and lower-limb BFR exercise, contralateral increases in muscular strength and task-related performance have been reported, indicating a systemic, crossover mechanism [71, [77][78][79][80]. Further mechanistic research into contralateral and proximal adaption following BFR exercise is warranted, although the existing research offers an opportunity for remote adaptation in complex clinical cases [74,81]. ...
... Blood flow restricted exercise and skeletal muscle health. Exerc Sport Sci Rev. 2009;37:[78][79][80][81][82][83][84][85]. h t t p s : / / d o i . ...
Background
Persistent pain is a complicated phenomenon associated with a wide array of complex pathologies and conditions (e.g., complex regional pain syndrome, non-freezing cold injury), leading to extensive disability and reduced physical function. Conventional resistance training is commonly contraindicated in load compromised and/or persistent pain populations, compromising rehabilitation progression and potentially leading to extensive pharmacological intervention, invasive procedures, and reduced occupational status. The management of persistent pain and utility of adjunct therapies has become a clinical and research priority within numerous healthcare settings, including defence medical services.
Main Body
Blood flow restriction (BFR) exercise has demonstrated beneficial morphological and physiological adaptions in load-compromised populations, as well as being able to elicit acute hypoalgesia. The aims of this narrative review are to: (1) explore the use of BFR exercise to elicit hypoalgesia; (2) briefly review the mechanisms of BFR-induced hypoalgesia; (3) discuss potential implications and applications of BFR during the rehabilitation of complex conditions where persistent pain is the primary limiting factor to progress, within defence rehabilitation healthcare settings. The review found BFR application is a feasible intervention across numerous load-compromised clinical populations (e.g., post-surgical, post-traumatic osteoarthritis), and there is mechanistic rationale for use in persistent pain pathologies. Utilisation may also be pleiotropic in nature by ameliorating pathological changes while also modulating pain response. Numerous application methods (e.g., with aerobic exercise, passive application, or resistance training) allow practitioners to cater for specific limitations (e.g., passive, or contralateral application with kinesiophobia) in clinical populations. Additionally, the low-mechanical load nature of BFR exercise may allow for high-frequency use within residential military rehabilitation, providing a platform for conventional resistance training thereafter.
Conclusion
Future research needs to examine the differences in pain modulation between persistent pain and pain-free populations with BFR application, supporting the investigation of mechanisms for BFR-induced hypoalgesia, the dose-response relationship between BFR-exercise and pain modulation, and the efficacy and effectiveness of BFR application in complex musculoskeletal and persistent pain populations.
... When training with BFR, the increase in BFR pressure typically decreases the workload necessary for increases in muscle size and strength (Jessee et al., 2018c). A proposed mechanism for muscular adaptations is muscle swelling (Jessee et al., 2018a), which can be measured by acute changes in muscle thickness (Loenneke et al., 2012b). ...
... A manual system (Hokanson AG101, E20 Cuff Inflator, and an MD6 Doppler probe) is commonly used in research to apply BFR based on the AOP. To assess AOP using a manual system, the pressure of the cuff needs to be increased until a detectable pulse (usually via the Doppler probe) distal to the cuff is no longer present (Jessee et al., 2018a;Abe et al., 2019). Previous research has shown that use of relative pressures based on a percentage of AOP and/or exercising until momentary failure seems to negate differences in the exercise response between different cuff widths (Bell et al., 2020) and manual systems . ...
The purpose of this study was to compare acute responses between manual and automated blood flow restriction (BFR) systems.
Methods
A total of 33 individuals completed this study. On visit 1, arterial occlusion pressure (AOP, mm Hg), cardiovascular responses, and discomfort (RPE-D) were measured with each BFR system at rest. On visit 2, unilateral bicep curls were completed [30% one-repetition maximum; 50% AOP] with one system per arm. Muscle thickness (MT, cm) and maximal force (N) were assessed before (pre), immediately (post-0), 5 min (post-5), and 10 min (post-10) post-exercise. Ratings of perceived exertion (RPE-E) and ratings of perceived discomfort (RPE-D) were assessed throughout the exercise. AOP and repetitions were compared with Bayesian paired t-tests. Other outcomes were compared with Bayesian RMANOVAs. BF10 represents the likelihood of the best model vs. the null. The results are presented as mean ± SD.
Results
Supine cardiovascular responses and RPE-D were similar for manual and automated (all BF10 ≤ 0.2). Supine AOP for manual (157 ± 20) was higher than that of automated (142 ± 17; BF10 = 44496.0), but similar while standing (manual: 141 ± 17; automated: 141 ± 22; BF10 = 0.2). MT (time, BF10 = 6.047e + 40) increased from Pre (3.9 ± 0.7) to Post-0 (4.4 ± 0.8; BF10 = 2.969e + 28), with Post-0 higher than Post-5 (4.3 ± 0.8) and Post-10 (4.3 ± 0.8; both BF10 ≥ 275.2). Force (time, BF10 = 1.246e + 29) decreased from Pre (234.5 ± 79.2) to Post-0 (149.8 ± 52.3; BF10 = 2.720e + 22) and increased from Post-0 to Post-5 (193.3 ± 72.7; BF10 = 1.744e + 13), with Post-5 to Post-10 (194.0 ± 70.6; BF10 = 0.2) being similar. RPE-E increased over sets. RPE-D was lower for manual than automated. Repetitions per set were higher for manual (Set 1: 37 ± 18; Set 4: 9 ± 5) than automated (Set 1: 30 ± 7; Set 4: 7 ± 3; all BF10 ≥ 9.7).
Conclusion
Under the same relative pressure, responses are mostly similar between BFR systems, although a manual system led to lower exercise discomfort and more repetitions.
... The mechanisms underlying the adaptations provided by training with BFR are still largely uncertain. It is speculated that the morphological adaptations resulting from the technique can be explained by the increased recruitment of motor units because of the severe fatigue elicited by the accumulation of metabolites caused by venous occlusion [9]. In addition, it has been theorized that cellular swelling secondary to pooling of blood from venous occlusion may activate muscle growth pathways [9,10]. ...
... It is speculated that the morphological adaptations resulting from the technique can be explained by the increased recruitment of motor units because of the severe fatigue elicited by the accumulation of metabolites caused by venous occlusion [9]. In addition, it has been theorized that cellular swelling secondary to pooling of blood from venous occlusion may activate muscle growth pathways [9,10]. ...
Purpose
It is recommended that the pressure applied in training with blood flow restriction (BFR) be relativized based on the arterial occlusion pressure (AOP). However, several factors can affect the measurement of AOP that may require consideration. The purpose of this review was to explore variables capable of impacting AOP and provide recommendations for measurement.
Methods
On August 8, 2023, PubMed® and Scopus databases were consulted to identify studies that analyzed variables capable of affecting AOP. In addition, the list of references of eligible studies, as well as Google Scholar citations, were consulted to identify additional studies.
Results
Twenty-three studies (n = 1335 participants) were included in this review. Studies analyzed the effects of cuff characteristics (n = 9), cuff bladder position (n = 1), body position (n = 6), inflation protocol (n = 1), time (n = 1), sex (n = 5), and segment (n = 5) on AOP. Results demonstrated that wider cuffs promote arterial occlusion with lower external pressures. In addition to width, cuff placement also affects AOP; when the bladder is positioned above the artery, less external pressure is needed to promote arterial occlusion. Body position significantly affects AOP, with more pronounced effects in the lower limbs. The time of day AOP is measured, but not the inflation protocol, has a significant effect on AOP. For the effect of sex and segment, results were divergent.
Conclusion
In conclusion, several factors may influence AOP. For standardizing the prescribed pressure in training with BFR, all these variables should be considered.
... These different BFR protocols may have an acute impact on post-exercise performance or muscle hypertrophy effects, with or without resistance exercise (Loenneke et al., 2012). Although the mechanisms underlying its effects have not been fully explored (Kubota et al., 2008), the phenomena initiating a cascade of physiological responses are triggered by the pooling of blood and fluid distal to the cuff, which enhances hydrostatic and osmotic gradients and finally increases intramuscular pressure and muscle volume (Jessee et al., 2018). ...
... The increase in muscle stiffness and frequency observed in the BFR condition may be related to higher intracellular fluid levels and the associated increase in intracellular fluid pressure. Such an increase in intracellular fluid levels is one of the physiological factors arising from the accumulation of fluid distal to the cuff, increasing hydrostatic and osmotic gradients, and ultimately increasing muscle volume and intramuscular pressure (Jessee et al., 2018), which are related with changes in the mechanical properties of muscles. Previous studies examining changes in the level of intracellular fluids during exercise performed under BFR (Wilk et al., 2018) could not separate the effect of exercise per se from the effect of BFR on the mechanical properties of the muscles involved. ...
Introduction: This study examined the effects of blood flow restriction (BFR) and reperfusion on the mechanical properties of the rectus femoris muscle at rest (frequency and stiffness).
Methods: Fourteen trained men (body weight = 81.0 ± 10.3 kg; BMI = 25 ± 3.0 m/kg²; height = 181 ± 4 cm; training experience = 6.0 ± 2.2 years) participated in an experimental session involving their dominant (BFR) and non-dominant leg (control). Muscle mechanical properties were measured using Myoton’s accelerometer at the midpoint of the rectus femoris muscle at five time points. In the BFR leg, an 80% arterial occlusion pressure was applied by a cuff for 5 min. No cuff was applied in the control leg. Femoral Myoton measurements were taken from both legs 2 and 4 min after the start of BRF as well as 30 s and 2 min after the end of the occlusion period.
Results: The two-way ANOVA revealed a statistically significant interaction effect for stiffness and frequency (p < 0.001; η² > 0.67). The post hoc analysis showed that both stiffness and frequency increased during BFR compared with rest and then dropped to the resting levels post BFR period. Also, stiffness and frequency were higher than control only during the BFR period, and similar during rest and post BFR.
Conclusion: These results indicate that the application of BFR at rest leads to significant changes in mechanical properties of the rectus femoris muscle.
... B lood flow restriction (BFR) is a technique that limits arterial and venous blood flow of the extremity with adaptable cuffs, while performing low intensity exercises. 1 In sport, BFR is used during resistance training with low loads (25-40% one-repetition maximum [1RM]). As benefits, this technique often generates similar muscle hypertrophy and strength responses than traditional high-load resistance training (70-85% 1RM). 2 Thus, it has been presented as an alternative methodology to be used in tandem with the use of high loads. ...
... In addition to the aforementioned mechanisms to explain gains on thigh circumference and strength after LL-BFR, other authors suggested greater protein synthesis mediated by mTORC1 as the explanation of increment of thigh girth. 1 Furthermore, LL-BFR could elicit the increment of angiogenesis mediated by the skeletal-muscle expression of mRNA. 31,32 Another reason to explain the gains of thigh girth may be the activity of the sympathetic nerve, and consequently, a higher secretion of growth hormone post LL-BFR. ...
Background:
The aim of this study is to evaluate the effectiveness of low-load blood flow restriction strength resistance training (LL-BFR) compared to high load strength resistance training (HL) on performance of professional soccer players.
Methods:
Eighteen male players from National Soccer Professional League were randomly allocated into two groups: LL-BFR, who performed a 6-weeks strength training program with low load (20-35% of one-repetition maximum-[1RM]), or HL, who performed a 6-week resistance training program with high load (70-85% 1RM). Before and after, thigh girth, vertical jump, lower limb strength, vertical force-velocity profile (F-v), and 30-m sprint were evaluated.
Results:
After the training program, both LL-BFR and HL induced significant increases compared to baseline in thigh girth (+3.3% for LL-BFR and +3.1% for HL) and maximal velocity during sprinting (+6.0 and +6.2%, respectively), without between-group differences. In reference to FV, only HL players improved imbalance (-54.4%), maximal theoretical force production (+10.4%) and decreased extension velocity (-20.5%) compared to baseline, without between-group differences. Only LL-BFR induced increases in maximum voluntary contraction of left hamstring compared to baseline (+13.8%), without between-group differences. No differences were shown for the rest of variables (P>0.05).
Conclusions:
Although LL-BFR may increase muscle circumference and sprint ability, these results are similar to those induced with HL in male professional soccer. In terms of F-v, only HL induced improvements, but these changes were not greater than those observed after LL-BFR.
... The main advantages of exercise with BFR compared to traditional exercise are: 1) increases in muscle size, strength, and aerobic capacity can be achieved with lower exercise intensities (Loenneke et al., 2012b;Bennett and Slattery, 2019;Clarkson et al., 2019), 2) adaptations from BFR occur faster, and 3) muscle size and strength can be increased with both aerobic and resistance exercise (Slysz et al., 2016). Although the exact mechanisms responsible for these adaptations are unknown, evidence (Jessee et al., 2018) suggests that increases in muscle size and strength are likely driven by cellular swelling and increased muscle activation occurring due to metabolite induced fatigue. Currently, increases in aerobic capacity are thought to occur via enhanced conduit artery blood flow, muscle capillary density, and muscle oxidative capacity in response to both the hypoxic stimulus during exercise and increased vascular shear stress upon cuff release (Formiga et al., 2020). ...
... Currently, increases in aerobic capacity are thought to occur via enhanced conduit artery blood flow, muscle capillary density, and muscle oxidative capacity in response to both the hypoxic stimulus during exercise and increased vascular shear stress upon cuff release (Formiga et al., 2020). A more comprehensive discussion surrounding the mechanisms responsible for adaptions to exercise with BFR are reviewed by Jessee and colleagues (Jessee et al., 2018) and Pignanelli and colleagues (Pignanelli et al., 2021). The following sections briefly discuss the effects of BFR-AE and BFR-RE on muscle size, muscle strength, and aerobic capacity and highlight unique advantages of these exercise modalities over that of high-intensity exercise without BFR in potentially managing the pathophysiology of COVID-19. ...
Accumulating evidence indicates that some COVID-19 survivors display reduced muscle mass, muscle strength, and aerobic capacity, which contribute to impairments in physical function that can persist for months after the acute phase of illness. Accordingly, strategies to restore muscle mass, muscle strength, and aerobic capacity following infection are critical to mitigate the long-term consequences of COVID-19. Blood flow restriction (BFR), which involves the application of mechanical compression to the limbs, presents a promising therapy that could be utilized throughout different phases of COVID-19 illness. Specifically, we hypothesize that: 1) use of passive BFR modalities can mitigate losses of muscle mass and muscle strength that occur during acute infection and 2) exercise with BFR can serve as an effective alternative to high-intensity exercise without BFR for regaining muscle mass, muscle strength, and aerobic capacity during convalescence. The various applications of BFR may also serve as a targeted therapy to address the underlying pathophysiology of COVID-19 and provide benefits to the musculoskeletal system as well as other organ systems affected by the disease. Consequently, we present a theoretical framework with which BFR could be implemented throughout the progression from acute illness to outpatient rehabilitation with the goal of improving short- and long-term outcomes in COVID-19 survivors. We envision that this paper will encourage discussion and consideration among researchers and clinicians of the potential therapeutic benefits of BFR to treat not only COVID-19 but similar pathologies and cases of acute critical illness.
... Similar partly ischaemic conditions occur during blood flow restriction (BFR) training (Jessee et al., 2018;Scott et al., 2016). During BFR, cuffs on the proximal part of the extremities occlude venous return and reduce arterial flow (Jessee et al., 2018). ...
... Similar partly ischaemic conditions occur during blood flow restriction (BFR) training (Jessee et al., 2018;Scott et al., 2016). During BFR, cuffs on the proximal part of the extremities occlude venous return and reduce arterial flow (Jessee et al., 2018). Recent research revealed that BFR training can elicit improvements in both strength (Scott et al., 2016) and endurance (Held et al., 2020 indices. ...
Grip and elbow flexor strength and endurance are crucial performance surrogates in competitive climbing. Thus, we examined the effects of blood flow restricted (BFR) climbing on grip and elbow flexor performance. Fifteen trained climbers (8 females; 20.8 ± 7.0 yrs; 1.72 ± 0.08 m; 63.0 ± 9.7 kg; 21.7 ± 2.7 IRCRCA grade) were either assigned to the intervention (BFR) or control (noBFR) group, using the minimization method (Strata: age, height, body mass, gender, and IRCRA grade). While BFR was used during low-intensity climbing training (2-times 10 min/session; 3-times/week), noBFR followed identical training protocols without BFR over 5 weeks. BFR of the upper limb was applied via customized pneumatic cuffs (occlusion pressure: 120 ± 23 mmHg, 75%; occlusion pressure). Endurance and strength performances were assessed via one-handed rung pulling (GripSTRENGTH), one-handed bent arm lock off at 90° (ArmSTRENGTH), static-intermitted finger hang (GripENDURANCE), and bent arm hang (ArmENDURANCE). Bayesian credible intervals revealed increased GripENDURANCE (+21 s (95% credible interval: -2 to 43 s)) and ArmENDURANCE +11 s (-5 to 27 s); adaptations via BFR. In contrast, GripSTRENGTH +4 N (-40 to 48 N) and ArmSTRENGTH +4 N (-68 to 75 N) were not affected by the BFR intervention. Fifteen cumulative sessions of BFR application with a cumulative total BFR load of 5 h over a 5 weeks macrocycle remarkably increased grip and elbow flexor endurance. Thus, BFR might serve as a promising means to improve relevant performance surrogates in trained climbers.
... However, in recent years, low-load blood flow restriction resistance training (LL-BFR) has gained increasing attention as a promising alternative (Burton, 2022;Hughes et al., 2017). Low-load blood flow restriction training (LL-BFR), which combines low external loads (20-30% 1RM) with partial blood flow restriction, induces metabolic stress and muscle fatigue, leading to adaptations in muscle strength, hypertrophy, and power that are comparable to those from high-load training (Jessee et al., 2018;Pearson & Hussain, 2015;Lixandrão et al., 2018). Therefore, LL-BFR training may provide a viable alternative to HLR training. ...
Background
Low-load blood flow restriction (LL-BFR) training has been shown to enhance muscle strength, power, and speed, but its effectiveness compared to traditional high-load resistance (HLR) training remains unclear. This meta-analysis aimed to compare the effects of LL-BFR and HLR training on muscle strength, power, and speed.
Methodology
Studies were identified by searching the SCOPUS, SPORTDiscus, PubMed, Web of Science, and CNKI databases up to May 13, 2024, using the following inclusion criteria: (a) healthy population; (b) comparison of LL-BFR vs HLR training; (c) pre- and post-training assessment of muscle strength (dynamic, isometric, and isokinetic), muscle power, jump, or speed performance; (d) PEDro scale score ≥4. The methodological quality of the included studies was assessed using the PEDro tool and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, with meta-analyses conducted using the R program.
Results
A total of 41 studies, involving 853 subjects, were included in the meta-analysis. Based on the PEDro scores and GRADE assessment, the overall quality of the included studies was assessed as moderate. LL-BFR training showed a slightly smaller effect on maximal strength compared to HLR training (ES = −0.19, 95% CI [−0.31 to −0.06], p < 0.01). There were no significant differences between LL-BFR and HLR training for muscle power (ES = −0.04, 95% CI [−0.33 to 0.24], p > 0.05), jump performance (ES = −0.08, 95% CI [−0.30 to 0.15], p > 0.05), and speed (ES = −0.28, 95% CI [−0.71 to 0.15], p > 0.05). Additionally, individual characteristics ( i.e ., age, gender, and training status) and training parameters ( i.e ., training duration, frequency, cuff pressure, and cuff width) did not significantly moderate the training effect.
Conclusions
LL-BFR training showed slightly less improvement in maximal strength compared to HLR training but demonstrated comparable effects on muscle power, jump performance, and speed in healthy individuals in healthy individuals. These findings suggest that LL-BFR may be a practical and effective alternative for individuals seeking performance improvements with lower training loads.
... It may be because BFR training can increase muscle hypertrophy, blood oxygen saturation, and glycolytic capacity, resulting in greater muscle adaptive capacity [56][57][58]. The increase in strength is believed to depend on the mechanism of muscle hypertrophy, and BFR can trigger two main mechanisms of skeletal muscle adaptation: cellular swelling [6] and metabolite accumulation [59]. It stimulated the synthesis of anabolic hormones, further recruits fast-twitch muscle fibers and leads to an increase in strength [60]. ...
Objective
To evaluate the effects of blood flow restriction (BFR) combined with endurance training on aerobic capacity, lower limb muscle strength, anaerobic power, and sports performance to supply effective scientific guidance for training. Two reviewers independently screened the literature, extracted data, and assessed the risk of bias of the included studies. We searched PubMed, Medline, Cochrane, SPORTDiscus and Web of Science databases up to 28 October 2024. Two reviewers independently screened the literature, extracted data, and assessed the risk of bias of the included studies. We calculated the effect size using standardized mean difference values and the random effects model. The results showed a medium effect size on maximal oxygen uptake (V̇O2max), a large effect size on lower limb muscle strength, a small effect size on anaerobic power and sports performance. In conclusion, while BFR training during endurance training had a significant positive effect on lower limb muscle strength and moderate improvement in V̇O2max, its impact on anaerobic power and sports performance was relatively small. These findings suggest that BFR training may be effective for enhancing muscle strength and aerobic capacity, but its benefits on anaerobic power and sport-specific performance may be limited. Therefore, it is important to carefully design BFR training programs to target specific outcomes.
... Theoretically, BFR works through several mechanisms, including the accumulation of anabolic metabolites, motor unit recruitment, and the release of catecholamines and growth hormone [4]. However, there is limited empirical evidence for these mechanisms, and there is some evidence that the same mechanisms may not affect muscle hypertrophy and strength [5]. ...
Purpose
This study aimed to determine the effect of low-weight resistance exercises performed with blood flow restriction (BFR) on muscle function in patients undergoing post-surgical rehabilitation following anterior cruciate ligament (ACL) reconstruction surgery.
Methods
Thirty-three patients who had undergone ACL surgery were included in the study. Patients were divided into 3 groups according to the sequential randomization method: low-weight resistance exercise with BFR, low-weight resistance exercise without BFR, and high-weight resistance exercise without BFR. All 3 groups were included in the exercise program for 12 sessions, 3 sessions per week for 4 weeks. As the first test, all participants underwent an isometric strength test on an isokinetic dynamometer device. After the 12th session of the exercise program, isometric strength test and isokinetic strength test were applied to all participants as the post-test.
Results
There was a significant increase in isometric muscle strength after the exercise protocol in all groups. When the isokinetic test results between the groups were compared; flexion maximum mean torque, flexion peak torque, flexion peak torque/body weight, and mean power parameters were between BFR + low-weight resistance exercise and low-weight resistance exercise groups; A statistically significant difference was found in favor of the BFR + low-weight resistance exercise group (p values 0.022; 0.031; < 0.001; 0.043, respectively).
Conclusion
Low-weight resistance exercises with BFR present a promising alternative for promoting early muscle strength development in patients recovering from ACL surgery.
... Blood flow restriction (BFR) training has gained increasing popularity in the fields of sports and rehabilitation (Hughes et al., 2017;Loenneke et al., 2010). This method involves applying an external constricting device to the proximal limbs to partially restrict venous return, thereby creating a hypoxic and stressful environment that promotes physical adaptations (Jessee et al., 2018). Previous metaanalyses have found that BFR resistance training can achieve effects similar to high-intensity resistance exercise, specifically regarding muscle strength and hypertrophy, while minimizing mechanical load (20-30% one repetition maximum) (Centner et al., 2019;Grønfeldt et al., 2020;Lixandrão et al., 2018). ...
Aerobic training with blood flow restriction (AT-BFR) has shown promise in enhancing both aerobic capacity and exercise performance. The aim of this review was to systematically analyze the evidence regarding the effectiveness of this novel training method on aerobic capacity, muscle strength, and hypertrophy in young adults. Studies were identified through a search of databases including PubMed, Scopus, Web of Science, SPORTDiscus, CINAHL, Cochrane Library, and EMBASE. A total of 16 studies, involving 270 subjects, were included in the meta-analysis. The results revealed that AT-BFR induced greater improvements in VO2max (SMD = 0.27, 95%CI: [0.02, 0.52], p < 0.05), and muscle strength (SMD = 0.39, 95%CI: [0.09, 0.69], p < 0.05), compared to aerobic training with no blood flow restriction (AT-noBFR). However, no significant effect was observed on muscle mass (SMD = 0.23, 95%CI: [-0.09, 0.56], p = 0.162). Furthermore, no moderating effects on the outcomes were found for individual characteristics or training factors. In conclusion, AT-BFR is more effective than AT-noBFR in improving aerobic capacity and muscle strength, making it a promising alternative to high-intensity training.
Systematic Review Registration
https://www.crd.york.ac.uk/prospero/, identifier CRD42024559872.
... -All participants used identical equipment, including high-concentration oxygen masks, weight materials, and cuffs (H-Cuff) [47,76]. -A second MVC test was conducted after the seventh session to establish a new MVC and adjust the workload. ...
Background and Objectives: This study investigates the effects of a five-week training program on the medial gastrocnemius muscle, comparing two approaches: blood flow restriction (BFR) training and normobaric hyperoxia (oxygen supplementation). It evaluates three strengthening modalities (dynamic, isometric, and the 3/7 method) analyzing their impact on maximal voluntary contraction (MVC), muscle architecture, and perceived exertion. Methods: A total of 36 young healthy participants (21 females, 15 males) were randomized into six subgroups (n = 6 each) based on the type of contraction and oxygen condition. Training sessions (three per week) were conducted for five weeks at 30% of MVC. Measurements of MVC, muscle circumference, pennation angle, fascicle length, and perceived exertion were taken at baseline (T0), mid-protocol (T1), and post-protocol (T2). Results: All groups demonstrated significant increases in MVC after five weeks, with no notable differences between BFR and oxygen conditions. Structural changes were observed in specific subgroups: the BFR-isometric group showed increased calf circumference (p < 0.05), and the 3/7 groups exhibited significant fascicle length gains (p < 0.05). Perceived exertion was consistently higher in BFR groups compared to oxygen supplementation, particularly in dynamic exercises. Conclusions: Both BFR and oxygen supplementation are effective in enhancing strength with light loads, though they elicit different structural and perceptual responses. Oxygen supplementation may be more comfortable and less strenuous, offering a viable alternative for populations unable to tolerate BFR. Future research should focus on optimizing training parameters and exploring applications tailored to specific athletic or clinical contexts.
... A physiological factor related to the alterations to the mechanical properties of the muscles is an increase in intramuscular pressure, accompanied by a higher level of intracellular fluid (Friden et al., 1986;Jarosz et al., 2023;Krzysztofik et al., 2023). Moreover, it affects muscle metabolism, tissue oxygenation and delays muscle recovery and function due to an impaired blood flow (Jessee et al., 2018;Kablan et al., 2021;Krzysztofik et al., 2023). Therefore, the overall performance is decreased. ...
The main goal of this study was to evaluate the effects of different reperfusion duration following intra-conditioning blood flow restriction (BFR) on bar velocity during the bench press exercise and muscle viscoelastic properties of the triceps brachii. Eleven resistance trained males (age: 24.3 ± 4.9 years; body mass: 85.5 ± 13.2 kg; bench press 1RM: 123.6 ± 25.4 kg; training experience: 6.8 ± 5.1 years) volunteered for the study. During experimental sessions participants performed 5 sets of 3 repetitions of the bench press exercise with a load of 60% 1RM under four different conditions: two BFR (80% AOP) and two control conditions. For the BFR conditions, cuffs were applied before each set for 4.5 min and released 30 or 60 s before the start of the set as reperfusion. Under the control conditions, BFR was not applied and the total duration of rest intervals amounted to 5 min and 5.5 min. Measurements of viscoelastic properties were conducted at baseline and immediately after completion of each set of the bench press exercise. The two-way ANOVA showed no significant condition × set interaction for mean and peak bar velocity (p = 0.93; p = 0.787; accordingly), and no main effect of condition for mean and peak bar velocity (p = 0.57; p = 0.417; accordingly). The Friedman's test showed no differences in oscillation frequency (p = 0.156), stiffness (p = 0.368), and the logarithmic decrement of tissue oscillation (p = 0.644). The results of this study indicate that BFR during rest intervals does not acutely influence mean and peak bar velocity, as well as mechanical properties of the triceps brachii regardless of the duration of reperfusion.
... pressure) is applied to the active limb. 11,12 These include factors such as cuff width, absolute applied pressure, duration of the pressure application and the potential interaction of these factors with participant characteristics such as limb circumference, adiposity, blood pressure and fitness. 2,13 In addition, the influence of these factors may vary depending on the nature of the exercise (e.g. ...
Objective
No study has examined outcomes derived from blood flow restriction exercise training interventions using regulated compared with unregulated blood flow restriction pressure systems. Therefore, we used a systematic review and meta-analyses to compare the chronic adaptations to blood flow restriction exercise training achieved with regulated and unregulated blood flow restriction pressure systems.
Data sources
The electronic database search included using the tool EBSCOhost and other online database search engines. The search included Medline, SPORTDiscus, CINAHL, Embase and SpringerLink.
Methods
Included studies utilised chronic blood flow restriction exercise training interventions greater than two weeks duration, where blood flow restriction was applied using a regulated or unregulated blood flow restriction pressure system, and where outcome measures such as muscle strength, muscle size or physical function were measured both pre- and post-training. Studies included in the meta-analyses used an equivalent non-blood flow restriction exercise comparison group.
Results
Eighty-one studies were included in the systematic review. Data showed that regulated (n = 47) and unregulated (n = 34) blood flow restriction pressure systems yield similar training adaptations for all outcome measures post-intervention. For muscle strength and muscle size, this was reaffirmed in the included meta-analyses.
Conclusion
This review indicates that practitioners may achieve comparable training adaptations with blood flow restriction exercise training using either regulated or unregulated blood flow restriction pressure systems. Therefore, additional factors such as device quality, participant comfort and safety, cost and convenience are important factors to consider when deciding on appropriate equipment to use when prescribing blood flow restriction exercise training.
... Blood flow restriction involves the application of a pneumatic cuff or elastic wrap to the most proximal portion of the limb, tightened to a point that reduces arterial inflow to the muscle, whilst largely preventing venous outflow from that same muscle region (10). Methods for applying blood flow restriction have differed across previous literature. ...
Song, JS, Hammert, WB, Kataoka, R, Yamada, Y, Kang, A, and Loenneke, JP. Individuals can be taught to sense the degree of vascular occlusion: Implications for practical blood flow restriction. J Strength Cond Res 38(8): 1413–1418, 2024—It is currently unknown if individuals can be conditioned to a relative arterial occlusion pressure (AOP) and replicate that pressure at a later time point. The purpose of this study was to determine whether individuals can be taught to sense a certain relative pressure (i.e., target pressure) by comparing a conditioning method with a time-matched non-conditioning control. Fifty-eight subjects completed 2 visits in a randomized order: (a) conditioning condition and (b) time-matched control condition. The conditioning involved 11 series of inflations to 40% AOP for 12 seconds followed by cuff deflation for 22 seconds. The pressure estimations were taken at 5 and 30 minutes after each condition. Data are presented as mean differences (95% credible interval). The absolute error at 5 minutes was greater for the control compared with conditioning condition (7.1 [2.0–12.1] mm Hg). However, this difference in absolute error between conditioning and control was reduced at 30 minutes (2.9 [−1.3 to 7.1] mm Hg). The mean difference and 95% limits of agreement for the control were 8.2 (−42.4 to 58.5) mm Hg at 5 minutes and 0.02 (−43.5 to 43.5) at 30 minutes. The agreements for the conditioning were −6.2 (−32.4 to 20.0) mm Hg at 5 minutes and −11.2 (−36.6 to 14.3) mm Hg at 30 minutes. The results suggest that the individuals can be taught to sense the target pressure, but this effect only lasts a short amount of time. Future work is necessary to refine the conditioning method to extend the duration of this conditioning effect.
... BFR in this situation offers a potentially practical stimulus to slow down the frequency of atrophy and preserve muscle strength. [4] The Sports Medicine Institute of America recommends resistance training between sixty and eighty percent of a 1RM for maximum strength and muscular growth improvements. However, high-intensity exercise is often not feasible due to various reasons. ...
... We opted for a work-matched design with external work (duration x intensity), with the aim of reducing the impact of external intensities on the results presented. Considering that perceptual responses can be affected by physiological variables and that adaptations after training with BFR may be related to fatigue (Jessee et al., 2018) and enhanced physiological stress (Smith et al., 2021), this study also performed comparisons between continuous LI-AE-BFR versus HIIE on acute post-exercise strength decline (measure of fatigue), and lactate and heart rate (HR) changes. ...
This study compared the effect of continuous low-intensity aero-bic exercise with blood flow restriction (LI-AE-BFR) versus high-intensity interval exercise (HIIE), matching total external mechanical work between conditions, on perceptual (exertion, pain, affective and pleasure) and physiological responses (heart rate [HR], blood lactate [BL] and muscle fatigue). Ten healthy untrained men (25.6 ± 3.78 years old; 75.02 ± 12.02 kg; 172.2 ± 6.76 cm; 24.95 ± 3.16 kg/m²) completed three visits to the laboratory. In visit 1, anthropometry, blood pressure and peak running velocity on the treadmill were measured. In visits 2 and 3, participants were randomly assigned to HIIE or LI-AE-BFR, both in treadmill. HIIE consisted of 10 one-minute stimuli at 80% of peak running velocity interspersed with one-minute of passive recovery. LI-AE-BFR consisted of 20-minutes of continuous walking at 40% of peak running velocity with bilateral cuffs inflated to 50% of arterial occlusion pressure. BL and maximum isometric voluntary contraction (MIVC-fatigue measure) were measured pre-and immediately post-exercise. HR, rating of perceived ex-ertion (RPE), and rating of perceived pain (RPP) were recorded after each stimulus in HIIE and every two minutes in LI-AE-BFR. Affective response to the session, pleasure, and future intention to exercise (FIE) were assessed 10 minutes after the intervention ended. Increases in BL concentrations were greater in HIIE (p = 0.028; r = 0.51). No effects time or condition were reported for MIVC. HR was higher in HIIE at all analyzed time points (p < 0.001; d = 3.1 to 5.2). RPE did not differ between conditions (p > 0.05), while average session RPP was higher in LI-AE-BFR (p = 0.036; r = 0.46). Affective positive response (p = 0.019; d = 0.9) and FIE (p = 0.013; d = 0.97) were significantly higher in HIIE. Therefore, HIIE elicited higher physiological stress, positive af-fective response, and intention to engage in future exercise bouts compared to LI-AE-BFR.
... Recent systematic reviews with meta-analysis have suggested that low-load resistance training (20-50% of one repetition maximum (RM)) combined with blood flow restriction to the exercising limb (low-load blood flow restricted resistance training: BFR-RT) and high-load resistance training (HL-RT, ≥ 70% 1RM) are equally effective in inducing gains in skeletal muscle mass in healthy populations ranging from young-to-old [1][2][3]. Therefore, BFR-RT has been suggested as a feasible exercise method in various clinical populations, where either fragile post-surgical conditions or the injury itself may restrict patients from exercising at higher muscle loading intensities [4,5]. Loss of skeletal muscle mass and strength due to immobilization or general unloading is a well-known challenge among patient populations [6][7][8]. ...
Objective
To compare the effect of low-load blood flow restricted resistance training (BFR-RT) versus high-load resistance training (HL-RT) on muscle strength, muscle mass, physical function, patient-reported outcomes, and adherence to training in clinical musculoskeletal populations.
Data sources
Web of Science, Cochrane Central, Medline, Embase, SportDiscus was searched on the 30 th May 2022.
Review methods
This study was conducted as a systematic review and meta-analysis. Randomized Controlled Trials (RCTs) were included if they (i) included patients, (ii) comprised of a BFR-RT intervention protocol and a group who performed HL-RT (≥ 70%1RM) for at least eight exercise sessions, and (iii) involved at least 1 exercise that targeted the lower limbs. The Cochrane Risk of Bias tool was used to evaluate the risk of bias. The meta-analyses were performed using a random effects model with an adjustment to the confidence interval.
Results
Seven RCTs comprising 303 participants (BFR-RT: n = 151; HL-RT: n = 152) were identified. HL-RT and BFR-RT showed similar gains in dynamic (1-10RM) knee extensor strength and leg press strength, quadriceps cross sectional area, sit-to-stand performance, and patient reported pain and function. There was a moderate effect favoring BFR-RT for increasing maximal isometric knee extensor strength. The grading of certainty in evidence was low-to-very low for all outcome variables.
Conclusion
This systematic review and meta-analysis extends our current knowledge about BFR-RT and HL-RT as equally effective exercise methods for inducing gains in maximal muscle strength in healthy populations, by now also comprising patients suffering from various clinical musculoskeletal conditions. The certainty in the estimates was low-to-very low, prompting the inclusion of future higher-quality trials.
Trial registration
PROSPERO ID (CRD42022337173). Registered June 18th 2022.
... 13 Recent research has shown that the use of low-intensity resistance training with BFR causes the hypertrophic adaptations needed, while also achieving comparable muscle adaptations typically seen in higher intensity resistance training. [13][14][15] Most studies used a low-intensity (50% 1MR) resistance training routine with BFR for the induction of muscle hypertrophy. [16][17][18] Skeletal muscle hypertrophy after a blood supply restriction is hypothesized to be caused by a variety of physiological processes. ...
b>Background: Blood flow restriction (BFR) therapy has emerged as a promising rehabilitation approach after knee surgery. The technique involves the use of a tourniquet or cuff to limit blood flow to the affected limb during low-resistance exercise, which creates a hypoxic environment thought to stimulate muscle growth and improve muscle function. Objective: Our scoping review aims to examine the current literature on the effectiveness of BFR combined with low-resistance exercise on rehabilitation after knee surgery. Method: The Google Scholar, PubMed, and PEDro databases were searched using relevant key-words. Studies that met the inclusion criteria were selected for analysis. The data from the selected studies were analyzed, categorized, and summarized to provide an overview of the findings. Results: In total, 12 studies met the inclusion criteria and were included in the review. Outcomes such as pain, strength, and range of motion were assessed. Conclusion: The results suggest that BFR and low-resistance exercise can be effective in improving patient outcomes following knee surgery. However, the heterogeneity of the studies made it difficult to determine the most effective approach. Further research is needed to identify the optimal dosage, frequency, and duration of BFR and low-resistance exercise for knee surgery rehabilitation.
... When combined with low-load resistance exercise (i.e., #30% 1 repetition maximum [1RM]), this form of training has been shown to induce changes in skeletal muscle size that are similar to traditional high-load resistance training (TRAD; i.e., 70% 1RM) (11,19,21,24). The mechanisms inherent to these adaptations are not fully understood but may stem from a complex interplay of reductions in oxygen delivery to the muscle (i.e., hypoxia), subsequent metabolite accumulation (e.g., lactate, inorganic phosphate, and/or hydrogen ions), and eventual recruitment of higher threshold motor units (20,37). The application of BFR, therefore, provides a reliable means through which low-load resistance training can be used to increase the muscle size (11,24,26). ...
Hammert, WB, Moreno, EN, Martin, CC, Jessee, MB, and Buckner, SL. Skeletal muscle adaptations to high-load resistance training with pre-exercise blood flow restriction. J Strength Cond Res XX(X): 000-000, 2023-This study aimed to determine if blood flow restriction (BFR) could augment adaptations to a high-load training protocol that was inadequate for muscle growth. Forty nontrained individuals had each arm assigned to 1 of 3 elbow flexion protocols: (a) high-load resistance training [TRAD; 4 sets to muscular failure at 70% 1 repetition maximum (1RM)], (b) low repetition high-load resistance training with pre-exercise BFR (PreBFR; 4 sets of 3 repetitions at 70% 1RM + 3 min of pre-exercise BFR), and (c) low repetition high-load resistance training (LRTRAD); 4 sets of 3 repetitions at 70% 1RM). Muscle thickness (MT), 1RM strength, and local muscular endurance (LME) of the elbow flexors were measured before and after 8 weeks. An alpha level of 0.05 was used for all comparisons. For the 50% site, MT increased for TRAD (0.211 cm, 95% confidence interval [95% CI]: 0.143-0.280), PreBFR (0.105 cm, 95% CI: 0.034-0.175), and LRTRAD (0.073 cm, 95% CI: 0.000-0.146). The change for TRAD was greater than PreBFR and LRTRAD. For the 60% site, MT increased for TRAD (0.235 cm, 95% CI: 0.153-0.317), PreBFR (0.097 cm, 95% CI: 0.014-0.180), and LRTRAD (0.082 cm, 95% CI: 0.000-0.164). The change for TRAD was greater than PreBFR and LRTRAD. For the 70% site MT increased for TRAD (0.308 cm, 95% CI: 0.247-0.369), PreBFR (0.103 cm, 95% CI: 0.041-0.166), and LRTRAD (0.070 cm, 95% CI: 0.004-0.137). The change for TRAD was greater than PreBFR and LRTRAD. One repetition maximum and LME significantly increased for each condition, with no differences between conditions. Collapsed across conditions 1RM strength increased 2.094 kg (95% CI: 1.771-2.416) and LME increased 7.0 repetitions (95% CI: 5.7-8.3). In conclusion, the application of BFR to low-repetition, high-load training did not enhance the adaptative response.
... Blood flow restriction (BFR) training is characterized by the application of inflatable cuffs, non-pneumatic elastic wraps or rigid nylon straps at the proximal portion of a limb during exercise in order to reduce arterial inflow and block venous return of blood in the respective extremity (Bielitzki et al. 2021). Its application is assumed to amplify intramuscular hypoxia (Biazon et al. 2019) (also known as localized hypoxia) distal to the cuff as a result of an inadequate oxygen supply and blood pooling (Jessee et al. 2018). Although the exact physiological mechanisms triggered by BFR training are not fully understood, it is thought that the external manipulation of blood flow leads to an increased level of metabolic stress (e.g., accumulation of inorganic phosphate) (Pearson and Hussain 2015). ...
Purpose:
This study investigated the acute effects of a static balance exercise combined with different blood flow restriction (BFR) pressures on motor performance fatigue development and recovery as well as physiological and perceptual responses during exercise in males and females.
Methods:
Twenty-four recreational active males (n = 13) and females (n = 11) performed static balance exercise on a BOSU ball (3 sets of 60 s with 30 s rest in-between) on three separate (> 3 days) laboratory visits with three different BFR pressures (80% arterial occlusion pressure [AOP], 40%AOP, 30 mmHg [SHAM]) in random order. During exercise, activity of various leg muscles, vastus lateralis muscle oxygenation, and ratings of effort and pain perception were recorded. Maximal squat jump height was measured before, immediately after, 1, 2, 4, and 8 min after exercise to quantify motor performance fatigue development and recovery.
Results:
Quadriceps muscle activity as well as ratings of effort and pain were highest, while muscle oxygenation was lowest in the 80%AOP compared to the 40%AOP and SHAM condition, with no differences in postural sway between conditions. Squat jump height declined after exercise with the highest reduction in the 80%AOP (- 16.4 ± 5.2%) followed by the 40%AOP (- 9.1 ± 3.2%), and SHAM condition (- 5.4 ± 3.3%). Motor performance fatigue was not different after 1 min and 2 min of recovery in 40% AOP and 80% AOP compared to SHAM, respectively.
Conclusion:
Static balance exercise combined with a high BFR pressure induced the largest changes in physiological and perceptual responses, without affecting balance performance. Although motor performance fatigue was increased by BFR, it may not lead to long-term impairments in maximal performance.
... Blood flow occlusion (BFO) superimposed on aerobic exercise is an evolving technique with the premise of enhancing aerobic capacity in athletic and clinical populations (Loenneke et al. 2010;Scott et al. 2015;Hughes et al. 2017;Jessee et al. 2018). In this technique, an inflated blood pressure cuff or tourniquet is applied to the proximal portion of the exercising limb to occlude venous and arterial blood flow in the working musculature. ...
Purpose
Constant blood flow occlusion (BFO) superimposed on aerobic exercise can impair muscle function and exercise tolerance; however, no study has investigated the effect of intermittent BFO on the associated responses. Fourteen participants (n = 7 females) were recruited to compare neuromuscular, perceptual, and cardiorespiratory responses to shorter (5:15s, occlusion-to-release) and longer (10:30s) BFO applied during cycling to task failure.
Methods
In randomized order, participants cycled to task failure (task failure 1) at 70% of peak power output with (i) shorter BFO, (ii) longer BFO, and (iii) no BFO (Control). Upon task failure in the BFO conditions, BFO was removed, and participants continued cycling until a second task failure (task failure 2). Maximum voluntary isometric knee contractions (MVC) and femoral nerve stimuli were performed along with perceptual measures at baseline, task failure 1, and task failure 2. Cardiorespiratory measures were recorded continuously across the exercises.
Results
Task failure 1 was longer in Control than 5:15s and 10:30s (P < 0.001), with no differences between the BFO conditions. At task failure 1, 10:30s elicited a greater decline in twitch force compared to 5:15s and Control (P < 0.001). At task failure 2, twitch force remained lower in 10:30s than Control (P = 0.002). Low-frequency fatigue developed to a greater extent in 10:30s compared to Control and 5:15s (P < 0.047). Dyspnea and Fatigue were greater for Control than 5:15s and 10:30s at the end of task failure 1 (P < 0.002).
Conclusion
Exercise tolerance during BFO is primarily dictated by the decline in muscle contractility and accelerated development of effort and pain.
... This is important as there appears to be a minimum amount of applied pressure (∼50% AOP) needed to induce fatigue accumulation during BFR exercise. 9 As fatigue is thought to be a primary mechanism of action in promoting the beneficial effects of BFR exercise, 10 applying a relative pressure of at least 50% AOP in the lower extremities is likely very important to eliciting the effects of BFR exercise. However, that assumes the restrictive cuff can apply 50% AOP. ...
A letter to the editor regarding a critical oversight in methodological design in Wang (2022). We discuss the challenges of extrapolating research algorithms from a single-chambered bladder system to a multi-chamber bladder system. We also highlight the implications of said methodological concern.
... low-intensity exercises with a pneumatic cuff applied to the proximal part of the lower limb to reduce the arterial blood flow to the extremity while blocking the venous outflow. BFR exercise has been suggested to improve aerobic capacity by increasing blood flow, the artery diameter, and the formation of capillaries [18][19][20][21][22] , but in patients with IC, the risk of deep venous thrombosis (DVT) has been a concern. However, no association has been reported between BFR exercise and increased cardiovascular morbidity [23][24][25][26] . ...
Unlabelled:
To examine the feasibility and safety of blood flow restricted walking (BFR-W) in patients with intermittent claudication (IC). Moreover, to evaluate changes in objective performance-based and self-reported functioning following 12 weeks of BFR-W.
Materials and methods:
Sixteen patients with IC were recruited from two departments of vascular surgery. The BFR-W programme implied the application of a pneumatic cuff around the proximal part of the affected limb at 60% limb occlusion pressure in five intervals of 2 min, four times per week for 12 weeks. Feasibility was evaluated by adherence and completion rates of the BFR-W programme. Safety was evaluated by adverse events, ankle-brachial index (ABI) at baseline and follow-up, and pain on a numerical rating scale (NRS pain) before and 2 min after training sessions. Furthermore, changes in performance between baseline and follow-up were evaluated with the 30 seconds sit-to-stand test (30STS), the 6-minute walk test (6MWT) and the IC questionnaire (ICQ).
Results:
Fifteen out of 16 patients completed the 12-week BFR-W programme and adherence was 92.8% (95% CI: 83.4; 100%). One adverse event unrelated to the intervention was reported causing one patient to terminate the programme 2 weeks prematurely. Mean NRS pain 2 min following BFR-W was 1.8 (95% CI [1.7-2]). ABI, 30STS, 6MWT and ICQ score were improved at follow-up.
Conclusions:
BFR-W is feasible and appears to be safe in terms of completion rate, adherence to the training protocol, and adverse events in patients with IC. Further investigation of the effectiveness and safety of BFR-W compared to regular walking exercise is needed.
... While analysing the effects of BFRT plus EX at intermediate and long term on muscle torque for isometric strength analysis during knee extension, a similar trend of improvement in strength and hypertrophy as of exercising with high intensity without occlusion was observed similarly in some studies (Amani-Shalamzari et al. 2019;Ramis et al. 2020) Studies indicate that during occlusion there might be the activation of type II muscle fibres (Loenneke et al. 2010). Subsequently, cell swelling leads to activation of the mechanistic target of rapamycin (mTOR) mitogen-activated protein kinase (MAPK) pathway (Loenneke et al. 2012), 40% decrease in expression of myostatin (Laurentino et al. 2012) and accumulation of metabolites (Jessee et al. 2018) which repress protein breakdown and enhance protein synthesis. ...
Background:
The benefits of Blood Flow Restriction Therapy (BFRT) have gained attention in recent times.
Objective:
This review aimed to evaluate the immediate (up to 24 hours), intermediate (up to 6 weeks), and long term (6-10 weeks) effects of BFRT plus exercises (EX) compared to EX only on athletic performance (sprint and jump performance), muscle strength, and hypertrophy in athletes and physically active population.
Methods:
A literature search was conducted to select randomized controlled trials across four electronic databases from inception till April 2021. The search yielded twenty-seven studies in total.
Results:
Based on eligibility criteria, twenty-one studies were analyzed. No differences were found between both groups for immediate (standardized mean difference [SMD] -0.02, 95% confidence interval [CI] -0.31, 0.27) and long-term effects (SMD -0.30, 95%CI -0.90, 0.30) on sprint performance. For jump performance, no significant effect was observed immediately (SMD -0.02 (95% CI -1.06, 1.02) and long term (SMD -0.40 (95% CI -1.46, 0.67). Similarly, muscle torque at intermediate (SMD 0.90 (95% CI -1.01, 2.81) and long term (SMD -0.54 (95% CI -1.19, 0.12), muscle strength at intermediate (SMD 1.12 (95% CI 0.20, 2.04) , and long term (SMD -0.07 (95% CI -0.56, 0.42) also showed non-significant effects. Muscle hypertrophy at intermediate (SMD 0.16 (95% CI -0.31, 0.63) and long term (SMD -0.20 (95% CI -0.90, 0.50) were not statistically significant.
Conclusions:
There was no significant difference observed in BFRT plus EX group compared to the EX-group on athletic performance, muscle strength, and muscle hypertrophy.
... Specifically, plasma concentrations of an opioid neuropeptide known as betaendorphin (BE) and the endocannabinoid endogenous ligand agonist 2-arachidonoylglycerol (2-AG) have recently been shown to be elevated following BFR exercise in humans (Hughes and Patterson, 2020;Hughes et al., 2021). Although there is a distinction between BFR and IPC, the similarities between these techniques involves overlapping mechanisms (Jessee et al., 2018;Patterson et al., 2019), which may implicate the involvement of these substances in the IPC response. Briefly, BE is thought to be released by the pituitary in response to stimulation of group III/IV afferents, thereby activating the opioid system and descending pain inhibitory pathways (Thoren et al., 1990;Hughes and Patterson, 2020). ...
Ischemic preconditioning (IPC) has been reported to augment exercise performance, but there is considerable heterogeneity in the magnitude and frequency of performance improvements. Despite a burgeoning interest in IPC as an ergogenic aid, much is still unknown about the physiological mechanisms that mediate the observed performance enhancing effects. This narrative review collates those physiological responses to IPC reported in the IPC literature and discusses how these responses may contribute to the ergogenic effects of IPC. Specifically, this review discusses documented central and peripheral cardiovascular responses, as well as selected metabolic, neurological, and perceptual effects of IPC that have been reported in the literature.
... Training with BFR is a new model of training that increases exercise intensity and provides similar or greater adaptations than high-intensity training. The primary physiological mechanism of BFR is tissue ischemia, which results in the accumulation of byproducts and cellular swelling, leading to the release of growth factors [27]. It was shown that training with BFR substantially increases blood lactate, growth hormone, and insulin-like growth factor-1 concentrations [28,29], which ultimately up-regulate protein synthesis, leading to maintaining or improving muscle mass. ...
Background
This study aimed to determine the efficacy of functional training with and without blood flow restriction (BFR) on muscle hypertrophy indices and strength in older men.
Methods
Thirty older adults (67.7 ± 5.8 years) were randomly assigned to three groups: functional training (FT), functional training with BFR (FTBFR), and control (C). Participants in experimental groups were trained in three sessions per week for six weeks. They performed 11 whole body exercises, in 2–4 sets of 10 repetitions. FTBFR group wore pneumatic cuffs on their extremities that began with 50% of estimated arterial occlusion pressure which increased by 10% every two weeks. Blood samples were obtained, and static strength tests were evaluated at baseline and after the training program. A One-Way Analysis of Covariance was used to interpret the data.
Results
A significant increase in follistatin levels ( p = 0.002) and reduction in myostatin levels ( p = 0.001) were observed in FT and FTBFR groups; there was a considerable increase in the F:M ratio in both training groups ( p = 0.001), whereas it decreased in C group. These changes were accompanied by significant improvements in handgrip ( p = 0.001) and shoulder girdle ( p = 0.001) strength in both experimental groups, especially in the FTBFR group. However, the levels of irisin were not statistically changed following interventions ( p = 0.561).
Conclusion
The findings showed that FT was effective in increasing circulating biomarkers involved in hypertrophy in older adults while adding BFR to FT had a slight increase in these biomarkers but had a tremendous increase in muscle strength.
... Several mechanisms may explain acute or long-term effects of LLRT-BFR in reducing pain, including (1) activating the endogenous opioid system via beta-endorphin, 31 (2) recruiting high threshold motor units (similar to high-load resistance training), 33 (3) a baroreceptor pathway due to increases in blood pressure, 30 and (4) a conditioned pain modulation phenomenon due to discomfort caused from the exercise loading. 30 In our study, the intensity and volume of the wrist extensors loading (minimum free weight with pain<2/10, 3 sets of 10 reps) differed to BFR best practice guidelines (30% of 1 RM, 4 sets of 30-15-15-15 reps) to avoid symptom flare-up due to the increased volume of loading. ...
OBJECTIVE: To evaluate the effect of low-load resistance training with blood flow restriction (LLRT-BFR) when compared to LLRT with sham-BFR in patients with lateral elbow tendinopathy (LET).
DESIGN: Randomized controlled trial.
METHODS: Forty-six patients with LET were randomly assigned to a LLRT-BFR or a LLRT with sham-BFR treatment group. All patients received soft tissue massage, supervised exercises with BFR or sham intervention (twice a week for 6 weeks), advice, and a home exercise program. The primary outcome measures were pain intensity, patient-rated tennis elbow evaluation (PRTEE) score, pain-free grip strength, and global rating of change, measured at baseline, 6 weeks, and 12 weeks. Between-group differences were evaluated using mixed-effects models with participant-specific random effects for continuous data. Global rating of change was analyzed using logistic regression.
RESULTS: Statistically significant between-group differences were found in favor of LLRT-BFR compared to LLRT with sham-BFR in pain intensity at 12-week follow-up (−1.54, 95% CI: −2.89 to −0.18; P = .026), pain-free grip strength ratio at 6-week follow-up (0.20, 95% CI: 0.06 to 0.34; P = .005), and PRTEE at 6- and 12-week follow-up (−11.92, 95% CI: −20.26 to −3.59; P = .006, and −15.23, 95% CI: −23.57 to −6.9; P<.001, respectively). At 6- and 12-weeks, patients in the LLRT-BFR group had greater odds of reporting complete recovery or significant improvement (OR = 6.0, OR = 4.09, respectively).
CONCLUSION: Low-load resistance training with blood flow restriction produced significantly better results compared to the LLRT with sham-BFR for all primary outcomes. Considering the clinically significant between-group improvement in function (>11 points in PRTEE) and the better success rates in the LLRT-BFR group, this intervention may improve recovery in LET. J Orthop Sports Phys Ther 2022;52(12):803–825. Epub: 14 September 2022. doi:10.2519/jospt.2022.11211
... In this way, a pneumatic cuff or elastic band is used to reduce blood flow and occlude venous return that induces an ischemic state in muscle tissue [2]. Resistance training has a high mechanical, low metabolic load [3]; however, during BFR, the metabolic load increases and elicits the same adaptations similar to heavy training [4]. Therefore, low-load resistance training with BFR is recommended to increase muscle mass. ...
Background
Resistance training with blood flow restriction (BFR) results in hypertrophy, and its magnitude depends on various training variables. This study aimed to compare the long-term effect of passive recovery (PR) and active recovery (AR) during low-intensity resistance training with BFR on hormonal levels and performance in young men.
Methods
In the randomized clinical trial, 20 men were randomly divided into PR and AR groups during resistance training with BFR. The intervention consisted of six upper and lower body movements with 30% of one maximum repetition (1RM), three sessions per week for six weeks. Both groups wore pneumatic cuffs on the proximal part of thighs and arms. The cuff pressure was 60% of the calculated arterial blood occlusion and increased 10% every two weeks. The AR group performed seven repetitions in 30 s break between sets by one second for concentric and eccentric phases and two seconds rest, and the other group had passive rest. The blood samples and a series of performance tests were gathered before and after the intervention. A repeated measure ANOVA was used to analyze data.
Results
AR and PR interventions significantly improved the C-reactive protein (CRP) (− 38% vs. − 40%), Lactate dehydrogenase (LDH) (− 11% vs. − 3%), Sargent jump (9% vs. 10%), peak power (20% vs.18%), and average power (14% vs. 14%), upper 1RM (8% vs. 8%) and no significant differences were observed between groups. The AR intervention significantly increased growth hormone (GH) (423% vs. 151%, p = 0.03), lower body 1RM (18% vs. 11%) and muscle endurance (34% vs. 22% for the upper body, p = 0.02 and 32% vs. 24% for the lower body, p = 0.04) than the PR group. The PR intervention further increased the minimum power than the AR group (19% vs. 10%). There were no significant changes in testosterone (p = 0.79) and cortisol (p = 0.34) following interventions.
Conclusion
The findings indicated that by increasing muscle activation and higher metabolic load, AR during resistance training with BFR might cause more remarkable improvements in serum GH, muscle strength, and endurance. Thus, to gain further benefits, AR during training with BFR is recommended.
Trial registration: IRCT20191207045644N1. Registration date: 14/03/2020. URL: https://www.irct.ir/search/result?query=IRCT20191207045644N1
... Although endurance improved after training with all conditions, differences in relative loads (15% versus 70% 1RM) and restriction pressures (0%, 40%, and 80% arterial occlusion pressure (AOP)) likely varied the stimulus across conditions. 3 This could mean that different adaptive mechanisms played a role in improved endurance between conditions. If this is the case, identifying the adaptive mechanisms from each training modality would be valuable for exercise prescription. ...
Objectives: To determine if different mechanisms, i.e., changes in one-repetition maximum (1RM) strength (Δ1RM) or vascular conductance (ΔVC), mediate changes in endurance (ΔEND) following training with 70% 1RM (70/0), 15% 1RM (15/0), and 15% 1RM with blood flow restriction using 40% (15/40) or 80% (15/80) arterial occlusion pressure. Design: Secondary analysis of data from a previous training intervention study. Method: Previously, 39 participants trained 2x/week for 8 weeks (4 sets of knee extensions to momentary failure) with 2 of the 4 aforementioned conditions (randomized, 1 per leg). VC, 1RM, and END were tested pre/post-training. A two-wave multiple-mediator model (adjusted for baseline values of 1RM, VC, and END) was constructed to evaluate direct and indirect effects of training on ΔEND (relative to other conditions) with Δ1RM and ΔVC as mediators. Results presented as coefficients (95%CI). Results: The model accounted for 35.3% (p < .001) of the variance in ΔEND. Relative direct effects on ΔEND did not differ across conditions (all p > .231). There was an effect of Δ1RM on ΔEND [0.5 (0.0,0.9) repetitions] and evidence that Δ1RM mediated the effect on ΔEND for 70/0 compared to other conditions [vs. 15/0 = 1.4 (0.1,2.9); 15/40 = 1.4 (0.1,2.7); 15/80 = 1.1 (0.1,2.3) repetitions]. There was no evidence of a relationship between ΔVC and ΔEND [0.02 (-0.10,0.13) repetitions] nor of relative indirect effects through ΔVC when comparing conditions. Conclusions: Differences in Δ1RM translate to increased endurance in the 70/0 condition compared to other conditions, however, differences in ΔVC did not appear to mediate increased endurance across the conditions.
... [2][3][4] BFR typically involves the application of a pressurized cuff, which is applied to the proximal portion of either the arms or legs with the intention of decreasing arterial blood flow to a working muscle, while largely restricting venous return. 5 Although blood flow restriction has been studied extensively, less is known regarding practical blood flow restriction (PBFR). PBFR involves, amongst others, the use of elastic bands as a wrapping device which applies pressure to the limb, resulting in a similar stimulus as more sophisticated pneumatic devices. ...
Practical blood flow restriction (PBFR) training has been used as a training technique to induce muscular strength and hypertrophy gains while utilizing lighter loads [≤ 40% one repetition maximum (1RM)]. It is unclear if PBFR can be incorporated into traditional training programs to alleviate some exposure to heavy loads. Objective: Compare the impact of a traditional resistance training with the addition of PBFR (TRAD + PBFR) to traditional resistance training without PBFR (TRAD) on maximal bench press and leg press strength. Design and Methods: Participants performed full body training for 4 weeks (2-3x/week). PBFR group performed 62% of sets blood flow restricted at 30% 1RM while the TRAD group performed all sets at an intensity of >70% 1RM. Results: Twenty-one resistance trained individuals (≥ 1 year resistance training) completed the study. For bench press strength, there was no group (TRAD + PBFR vs. TRAD) by time (pre vs. post) interaction (BF10 = 0.32). However, there was a main effect for time (BF10 = 24.04). The TRAD + PBFR group increased strength from 99 ± 29 to 106 ± 23 kg and the traditional training condition increased from 111 ± 27 to 117 ± 24kg. For leg press strength, there was no interaction (BF10 = 0.83). However, there was a main effect for time, with both conditions increasing strength. For the PBFR group strength increased from 372 ± 61 to 423 ± 76 kg and the TRAD group increased strength from 354 ± 87 to 434 ± 96kg. Conclusion: TRAD + PBFR elicited similar strength adaptations compared to TRAD. PBFR may provide a means to exposing the muscle and connective tissue to less overall mechanical stress when incorporated into a traditional heavy resistance training program.
This study analysed perceived exertion (RPE) and blood lactate ([La−]) responses to two resistance training protocols planned with high- (HLI) and low-load intensities combined with blood flow restriction (LLI+BFR). Fourteen trained adults (26.2 ± 2.6 years) performed the HLI and LLI+BFR protocols 48 h apart. The HLI was planned with 70% 1RM (one repetition to maximum), three sets, 12 repetitions, 60 seconds (s) of rest between sets and 120 s between exercises; LLI+BFR was performed at 30% 1RM, for three sets, 15 repetitions, and with 30 s of rest between sets and 180 s between exercises. Blood samples (for [La−] analysis) and RPE (Borg 0–10 scale) were collected in the first minute after each exercise. A two-way ANOVA compared RPE and [La−] responses between exercises in the same protocol, and between protocols comparing the same exercise. RPE increased from the first to the last half (involving upper-limbs and lower-limbs) of exercises in both protocols (p < 0.001). All exercises in HLI elicited higher RPE values than LLI+BFR (p < 0.001). Average RPE scores were higher in HLI than for LLI+BFR (8.1 ± 0.6 > 6.2 ± 1.1, p < 0.001). The [La−] also increased throughout the exercises, with a higher peak response in LLI+BFR than for HLI (9.8 ± 1.6 > 7.2 ± 1.3 mmol × L−1, p < 0.01). Perceptual and metabolic responses during HLI and LLI+BFR training were distinguishable, despite both protocols characterising a high-intensity stimulus.
Background
Delayed onset muscle soreness (DOMS) is a well‐established phenomenon characterized by ultrastructural muscle damage that typically develops following unfamiliar or high‐intensity exercise. DOMS manifests with a constellation of symptoms, including muscle tenderness, stiffness, edema, mechanical hyperalgesia, and a reduced range of joint motion. In recent years, the application of blood flow restriction (BFR) has garnered attention for its potential impact on DOMS.
Objective
This study aimed to investigate the effects of different BFR intensities on biomechanical alterations induced by DOMS in healthy individuals.
Design and Methods
Thirty participants were split into two groups receiving either 80% or 20% BFR applied during low‐intensity resistance exercise following DOMS induction. Pain perception, pressure pain threshold, muscle biometric characteristics, and strength were assessed before DOMS, after DOMS, and following BFR application at 24, 48, and 72 h.
Results
The 80% BFR group experienced faster reductions in pain perception compared to the 20% BFR group. Muscle strength recovery was also statistically faster in the 80% BFR group. No significant differences were observed between groups in muscle stiffness, flexibility, or other mechanical properties.
Conclusions
These findings suggest that BFR, particularly at higher intensities, may alleviate DOMS symptoms and accelerate muscle strength recovery. However, the lack of a control group and limitations in muscle property assessment warrant further research to definitively determine BFR's efficacy in managing DOMS.
Blood flow restriction (BFR) has been identified as a potential countermeasure to mitigate physiological deconditioning during spaceflight. Guidelines recommend that tourniquet pressure be prescribed relative to limb occlusion pressure (LOP); however, it is unclear whether body tilting or reduced gravity analogues influence LOP. We examined LOP at the leg and arm during supine bedrest and bodyweight suspension (BWS) at 6° head‐down tilt (HDT), horizontal (0°), and 9.5° head‐up tilt (HUT) positions. Twenty‐seven adults (age, 26 ± 5 years; height, 1.75 ± 0.08 m; body mass, 73 ± 12 kg) completed all tilts during bedrest. A subgroup (n = 15) additionally completed the tilts during BWS. In each position, LOP was measured twice in the leg and arm using the Delfi Personalized Tourniquet System after 5 min of rest and again after a further 5 min. The LOP at the leg increased significantly from 6° HDT to 9.5° HUT in bedrest and BWS by 9–15 mmHg (Cohen's d = 0.7–1.0). Leg LOP was significantly higher during BWS at horizontal and 9.5° HUT postures relative to the same angles during bedrest by 8 mmHg (Cohen's d = 0.6). Arm LOP remained unchanged between body tilts and analogues. Intraclass correlation coefficients for LOP measurements taken after an initial and subsequent 5 min rest period in all conditions ranged between 0.91–0.95 (leg) and 0.83–0.96 (arm). It is advised that LOP be measured before the application of a vascular occlusion in the same body tilt/setting to which it is applied to minimize discrepancies between the actual and prescribed tourniquet pressure.
The intricate architecture of skeletal muscle, characterized by myriad fibers with distinct functional and metabolic properties, plays a pivotal role in orchestrating force generation and endurance capabilities in response to diverse demands. Among the different fibers, type 1 and type 2 fibers emerge as the protagonists, each endowed with unique attributes for varying requirements of muscle performance. Type 1 fibers, often heralded as the marathoners of muscle fibers, exhibit a remarkable proficiency in sustained aerobic activities, courtesy of their abundant mitochondrial content and propensity for oxidative metabolism. Conversely, type 2 fibers, the sprinters of the muscular realm, are tailored for rapid, high-intensity bursts of activity, relying predominantly on glycolytic pathways for their energetic needs. This dichotomy in functional specialization is underpinned by a molecular framework that tailors each fiber type to its specific role. This framework includes the nuanced expression and regulation of mechanosensors and signaling molecules pivotal for muscle adaptation and homeostasis.
BACKGROUND: Pain and weakness are 2 commonly reported postamputation symptoms. The purpose of this case report is to propose a novel blood flow restriction (BFR) protocol to address pain and weakness in a patient with transtibial limb loss.
CASE PRESENTATION: A 36-year-old male 2 months after transtibial amputation presented for evaluation and treatment of his postamputation pain, weakness, and poor functional mobility. The patient completed a novel BFR strength protocol twice per week for 12 weeks.
OUTCOME AND FOLLOW-UP: Amputee Mobility Predictor, L Test Measure of Functional Mobility, 2-minute walk test, 30-second sit to stand, hamstring force, single-limb leg press repetition maximum, hip abduction endurance test, and numeric pain scale preintervention and postintervention were measured. The patient achieved the minimal detectable change for the L-Test and 2MWT, resulting in meaningful improvement in the patient’s strength and function following the blood flow restriction protocol.
DISCUSSION: This case supports the use of blood flow restriction to address postamputation weakness and pain in a physical therapy setting. JOSPT Cases 2024;4(1):1-7. Epub 30 November 2023. doi:10.2519/josptcases.2023.11327
Objective:
To compare the acute psychophysiological responses to blood flow restriction (BFR) exercise using a traditional research device or novel, automated system.
Methods:
Forty-four resistance trained individuals performed four sets of unilateral elbow flexion exercise [30% one-repetition maximum (1RM)] to volitional failure using two distinct restrictive devices [SmartCuffs PRO BFR Model (SMARTCUFF), Hokanson E20 Rapid Inflation device (HOKANSON)] and with two levels of BFR [40% limb occlusion pressure (LOP), 80% LOP]. Blood pressure (BP), muscle thickness (MT), and isometric strength (ISO) were assessed prior to and following exercise. Perceptual responses [ratings of perceived exertion (RPE), discomfort] were assessed prior to exercise and following each exercise set.
Main Results:
Data are displayed as means (SD). Immediately following exercise with 40% LOP, there were no statistical differences between devices for BP, MT, and ISO. However, only following Set 1 of exercise, RPE was greater with SMARTCUFF compared to HOKANSON (p < 0.05). In addition, only following Set 2 of exercise, discomfort was greater with HOKANSON compared to SMARTCUFF (p < 0.001). Immediately following exercise with 80% LOP, there were no statistical differences between devices for BP, MT, and ISO. However, only following Set 4 of exercise, RPE was greater with HOKANSON compared to SMARTCUFF (p < 0.05). In addition, following all exercise sets, discomfort was greater with HOKANSON compared to SMARTCUFF (p < 0.001). Significance: The present study provides valuable insight into the efficacy of a novel, automated BFR system (SMARTCUFF) eliciting comparable acute physiological responses to BFR exercise and in some cases favorable psychological responses when compared to a traditional research device (HOKANSON).
Background and Purpose: Resistance training (RT) is an effective program for creating hormonal, functional and structural adaptations, so that manipulation of its variables induces different adaptations. Change in the secretion rate and serum level of hormones due to resistance activity is the main factor in protein synthesis and hypertrophy of skeletal muscles, so the purpose of this study was to investigate hypertrophic and hormonal responses to a session of resistance training with two different protocols in male sprint runner. Materials and Methods: 45 men volunteers (age: 21± 1.7 year, weight: 67.5± 4.35 kg and BMI: 22 ± 1.03 kg/m2) were randomly divided in to three groups of 15 people (high-load training, low-load training and control). The training protocol includes seven movements (chest press with barbell, leg extension, biceps barbell, standing shoulder press with barbell, Seated leg machine, Lat pull down and Triceps machine), three sets with 70% 1-RM to failure for training group with high load, seven movements (chest press with barbell, leg extension, biceps barbell, standing shoulder press with barbell, Seated leg machine, Lat pull down and Triceps machine), three sets with 30% 1-RM to failure for training group with low load and no activity for control group. Thickness of biceps and vastus lateralis and serum levels of cortisol, IGF-1, testosterone hormones and testosterone/cortisol (T/C) ratio were measured at two stages (pre-test and 30 minute after the RT). The Shapiro-Wilk and the Levine tests were performed to confirm the normality of data distribution and the homogeneity of variances, respectively. Results: The result of paired-sample t test showed serum concentration of testosterone (P=0.005), IGF-1 (P=0.004), cortisol (P=0.020), T/C (P<0.001), thickness of biceps (P=0.001) and thickness of vastus later-alis (P=0.001) were increased only in RT group with high load compared to the pre-test. Also, the results of ANOVA and Bonferroni's post hoc test showed the mean of serum concentration of testosterone, IGF-1, cortisol, T/C, thickness of biceps and vastus lateralisin high-load training group was significantly higher than the low-load training (P ≤ 0.05) and control (P ≤ 0.05) groups in the post-test. Conclusion: Although one session of resistance training with an intensity of 30% of 1RM did not cause a significant change in the serum level of hormones and hypertrophy, it seems that hypertrophy produced after a 70% of 1-RM acute resistance training protocol (and with repetition to failure) appears to be due to hormonal changes due to metabolic stress.
Athletes can experience loss of muscle mass and function for multiple reasons following a sports injury, surgery, fracture, or joint degeneration. High load resistance training is often contraindicated early on in rehabilitation. Low-load blood flow restriction (BFR) training has beneficial effects on skeletal muscle strengthening while avoiding the risks of heavy loads. BFR can be used in a wide range of clinical applications including prehabilitation, rehabilitation, potentially reducing return to sport timelines. It may assist athletes looking for those marginal gains when their current training program has plateaued. Managing or preventing musculoskeletal injuries in a sports setting can be challenging with a plethora of modalities and options to facilitate rehabilitation and recovery. Dry Needling and Cupping Therapy may be beneficial in reducing pain. While cryotherapy can be used for pain relief and recovery, it has recently been discouraged in the management of acute soft tissue injuries. New innovations in manual therapy, including foam rolling, percussive massage devices, and instrument-assisted soft tissue mobilization, extrapolate their benefit primarily from sports massage promoting pain relief, increased flexibility, and faster recovery. They are popularized for allowing “self-massage.” Muscle energy and active release techniques aim to reduce pain, increase range of motion (ROM) and facilitate optimal tissue healing. All these innovations may have a role in managing an endurance athlete through rehabilitation, training, competition, recovery, and injury prevention; however most require more high quality research with greater homogeneity across samples, methods, measurements, and treatment protocols in the future.KeywordsBlood flow restrictionCuppingDry needlingPercussive massageInstrument-assisted massageCryotherapyFoam rollingMETRecoverySelf-massageMassage device
Training with blood flow restriction (BFR) has been shown to be a useful technique to improve muscle hypertrophy, muscle strength and a host of other physiological benefits in both healthy and clinical populations using low intensities [20%–30% 1-repetition maximum (1RM) or <50% maximum oxygen uptake (VO2max)]. However, as BFR training is gaining popularity in both practice and research, there is a lack of awareness for potentially important design characteristics and features associated with BFR cuff application that may impact the acute and longitudinal responses to training as well as the safety profile of BFR exercise. While cuff width and cuff material have been somewhat addressed in the literature, other cuff design and features have received less attention. This manuscript highlights additional cuff design and features and hypothesizes on their potential to impact the response and safety profile of BFR. Features including the presence of autoregulation during exercise, the type of bladder system used, the shape of the cuff, the set pressure versus the interface pressure, and the bladder length will be addressed as these variables have the potential to alter the responses to BFR training. As more devices enter the marketplace for consumer purchase, investigations specifically looking at their impact is warranted. We propose numerous avenues for future research to help shape the practice of BFR that may ultimately enhance efficacy and safety using a variety of BFR technologies.
Introduction:
The use of blood flow restriction (BFR) has been shown to promote greater increases in muscle size and strength when applied during low intensity aerobic exercise and low load resistance exercise. Whether BFR can enhance the effectiveness of E-STIM has been less explored and is the purpose of this study.
Evidence acquisition:
The databases of Pubmed, Scopus, and Web of Science were searched using the following search: "blood flow restriction" OR "occlusion training" OR "KAATSU" AND "electrical stimulation" OR "E-STIM" OR "neuromuscular electrical stimulation" OR "NMES" OR "electromyostimulation." A three-level random effects restricted maximum likelihood model was computed.
Evidence synthesis:
Four studies met the inclusion criteria. There was no additive effect of performing E-STIM under BFR when compared to E-STIM in the absence of BFR [ES: 0.88 (95% CI: -0.28, 2.05); P=0.13]. There was a greater increase in strength when E-STIM was performed under BFR as compared to the same protocol without BFR [ES: 0.88 (95% CI: 0.21, 1.54); P=0.01].
Conclusions:
The lack of effectiveness for BFR to enhance muscle growth may be related to the non-orderly recruitment of motor units when performing E-STIM. The ability of BFR to augment increases in strength may also allow individuals to utilize lower amplitudes to reduce participant discomfort.
Purpose:
The purpose was to examine the physiological responses resulting from an acute blood flow restriction (BFR) resistance exercise bout with two different cuff pressures in young, healthy men and women.
Methods:
Thirty adults (18-30 yr) completed a bilateral leg extension BFR bout consisting of four sets (30-15-15-15 repetitions) with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and electromyographic amplitude (EMG AMP) were collected from the dominant or non-dominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVAs were used to examine mean differences in the change in EMG AMP and NIRS-parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A p-value ≤0.05 was considered statistically significant.
Results:
Regardless of sex or cuff pressure, the change in EMG amplitude was lower in set 1 (14.8%) compared to the remaining sets (22.6 - 27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP there was an effect for Time such that MAP increased from pre (87.5 ± 4.3 mmHg) to post-exercise (104.5 ± 4.1 mmHg).
Conclusions:
The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the inter-set rest. Additionally, there did not appear to be any meaningful sex-related difference in this sample of young healthy adults.
Purpose:
To examine the acute muscular and cardiovascular responses to applying blood flow restriction (BFR) prior to high-load training.
Methods:
40 trained individuals visited the lab on 3 occasions. On visit 1, participants completed paperwork and performed strength assessments. During Visits 2 and 3 participants completed 4 exercise conditions (one in each arm during each visit): 1) Traditional resistance training (TRAD), 2) Low load training with BFR (LLBFR), 3) Low repetition high load training with pre-exercise BFR (PreBFR), 4) Low repetition traditional training (LRTRAD). Blood pressure, muscle thickness (MT), and isometric torque (ISO) were measured before and after exercise.
Results:
Data is displayed as means (SD). Immediately following exercise, MT in TRAD was greater compared to PreBFR [mean difference = 0.18(0.30)cm, p<0.001] and LRTRAD [mean difference =0.28(0.30)cm, p<0.001]. In addition, LLBFR demonstrated greater MT compared to PreBFR [mean difference =0.24(0.30) cm,p< 0.001]. Immediately following exercise, ISO was lower in TRAD compared to PreBFR [mean difference = 33.8(46.9)N,p<0.001] and the LRTRAD condition [mean difference = 32.8(50.4)N,p<0.001]. In addition, ISO was lower in LLBFR compared to PreBFR [mean difference = 43.9 (47.4)N,p< 0.001] and LRTRAD [mean difference = 42.9 (43.8)N, p < 0.001]. Immediately following exercise, systolic blood pressure was greater in TRAD compared to PreBFR and LRTRAD.
Conclusion:
The application of BFR prior to engaging in high-load training does not seem to augment the muscular responses to exercise when compared to traditional high loads alone; however, it may pose less demand on the cardiovascular system. This article is protected by copyright. All rights reserved.
Purpose: To 1) examine whether blood flow restriction would provide an additional exercise-induced hypoalgesic response at an upper and lower limb when it is incorporated with low-load resistance exercise until failure, and 2) examine if increases in blood pressure and discomfort, with blood flow restricted exercise, would mediate the exercise-induced hypoalgesia over exercise without blood flow restriction. Methods: Forty healthy young participants completed two trials: four sets of unilateral knee extension exercise to failure at 30% of one-repetition maximum, with and without blood flow restriction. Pressure pain thresholds were assessed before (twice) and 5-min post exercise at an upper and lower limb. Blood pressure and discomfort ratings were recorded to examine mediating effects on exercise-induced hypoalgesia with blood flow restricted exercise. Results: Pressure pain threshold increased following both exercise conditions compared to a control, without any differences between exercise conditions at the upper (exercise conditions vs. control: ~0.37 kg/cm²) and lower (exercise conditions vs. control: ~0.60 kg/cm²) limb. The total number of repetitions was lower for exercise with blood flow restriction compared to exercise alone [median difference (95% credible interval) of −27.0 (−29.8, −24.4) repetitions]. There were no mediating effects of changes in blood pressure, nor changes in discomfort, for the changes in pressure pain threshold at either the upper or lower limb. Conclusion: The addition of blood flow restriction to low-load exercise induces a similar hypoalgesic response to that of non-blood flow restricted exercise, with a fewer number of repetitions.
Background and purpose:
Individuals with Multiple Sclerosis (MS) often present with weakness, poor balance, and increased fatigue that affects physical function. Blood flow restriction training (BFRt) is a popular treatment method to improve strength in orthopedic patients. However, research is limited on the use of BFRt for individuals with MS. This case report describes the effects of BFRt for an individual with relapsing-remitting MS (RRMS).
Case description:
A 30-year-old female with RRMS presented to physical therapy (PT) with weakness and balance difficulty. Initial PT interventions were ineffective at improving balance and strength to achieve specific functional standing and balance goals. BFRt was introduced at reevaluation and performed 2×/week for 8 weeks. Activities-specific Balance Confidence Scale, Modified Fatigue Impact Scale, Berg Balance, strength, and 10-meter walk were assessed at 4 and 8 weeks.
Outcomes:
Measures of strength and balance improved with the addition of BFRt and no adverse events occurred. The addition of BFRt resulted in a meaningful improvement in the individual's ability to achieve her standing and balance goals.
Discussion:
This case report describes the successful application of BFRt to improve function in an individual with RRMS. Further research is warranted for the use of BFRt for individuals with MS.
Objective: Identify whether the application of blood flow restriction (BFR) during walking influences fraction of expired oxygen (FeO2) and carbon dioxide (FeCO2) measures, key variables in the calculation of oxygen consumption (V̇O2) via indirect calorimetry.
Design: Randomised cross-over.
Methods: On separate visits, sixteen participants completed four experimental sessions (order randomised), each comprising 10 min of treadmill exercise; i.e., with or without BFR (60% arterial occlusion pressure) combined with two different intensity levels (100% or 120% comfortable walking speed). For data analysis, walking speeds within the same condition (with or without BFR) were pooled, and the speed variance was controlled within the statistical model. The FeO2, FeCO2, V̇O2, volume of carbon dioxide production, minute ventilation (V̇E) and respiratory exchange ratio were extracted from the metabolic cart from the fifth min of the exercise period to the 3 min post-exercise. Measures were averaged across 2 min increments during exercise and 1 min increments post-exercise.
Results: Condition × time interactions were observed for FeO2 (p<0.01) and FeCO2 (p<0.01). Post hoc analysis identified within the BFR condition an increase in FeO2 (p<0.01) during the exercise period and for 2 min post-exercise, while FeCO2 was decreased (p<0.01) during the exercise period and 1 min post-exercise. A main effect of BFR and time was observed for V̇E (p≤0.044) and V̇O2 (p≤0.01).
Conclusions: The increase of FeO2 and decrease of FeCO2 during BFR walking likely reduces the validity of V̇O2 values calculated via indirect calorimetry.
Resistance-based blood flow restriction training (BFRT) improves skeletal muscle strength and size. Unlike heavy-load resistance training (HLRT), there is debate as to whether strength adaptations following BFRT interventions can be primarily attributed to concurrent muscle hypertrophy, as the magnitude of hypertrophy is often minor. The present study aimed to investigate the effect of 7 weeks of BFRT and HLRT on muscle strength and hypertrophy. The expression of protein growth markers from muscle biopsy samples was also measured. Male participants were allocated to moderately heavy-load training (HL; n = 9), low-load BFRT (LL + BFR; n = 8), or a control (CON; n = 9) group to control for the effect of time. HL and LL + BFR completed 21 training sessions (3 d.week⁻¹) comprising bilateral knee extension and knee flexion exercises (HL = 70% one-repetition maximum (1-RM), LL + BFR = 20% 1-RM + blood flow restriction). Bilateral knee extension and flexion 1-RM strength were assessed, and leg muscle CSA was measured via peripheral quantitative computed tomography. Protein growth markers were measured in vastus lateralis biopsy samples taken pre- and post the first and last training sessions. Biopsy samples were also taken from CON at the same time intervals as HL and LL + BFR. Knee extension 1-RM strength increased in HL (19%) and LL + BFR (19%) but not CON (2%; p < 0.05). Knee flexion 1-RM strength increased similarly between all groups, as did muscle CSA (50% femur length; HL = 2.2%, LL + BFR = 3.0%, CON = 2.1%; TIME main effects). 4E-BP1 (Thr37/46) phosphorylation was lower in HL and LL + BFR immediately post-exercise compared with CON in both sessions (p < 0.05). Expression of other growth markers was similar between groups (p > 0.05). Overall, BFRT and HLRT improved muscle strength and size similarly, with comparable changes in intramuscular protein growth marker expression, both acutely and chronically, suggesting the activation of similar anabolic pathways. However, the low magnitude of muscle hypertrophy was not significantly different to the non-training control suggesting that strength adaptation following 7 weeks of BFRT is not driven by hypertrophy, but rather neurological adaptation.
Purpose:
To test the effects of 4 weeks of unilateral low-load resistance training (LLRT), with and without blood flow restriction (BFR), on maximal voluntary contraction (MVC), muscle thickness, volitional wave (V wave), and Hoffmann reflex (H reflex) of the soleus muscle.
Methods:
Twenty-two males were randomly distributed into three groups: a control group (CTR; n = 8); a low-load blood flow restriction resistance training group (BFR-LLRT; n = 7), who were an inflatable cuff to occlude blood flow; and a low-load resistance training group without blood flow restriction (LLRT; n = 7). The training consisted of four sets of unilateral isometric LLRT (25% of MVC) three times a week over 4 weeks.
Results:
MVC increased 33% (P < 0.001) and 22% (P < 0.01) in the trained leg of both BFR-LLRT and LLRT groups, respectively. The soleus thickness increased 9.5% (P < 0.001) and 6.5% (P < 0.01) in the trained leg of both BFR-LLRT and LLRT groups, respectively. However, neither MVC nor thickness changed in either of the legs tested in the CTR group (MVC -1 and -5%, and muscle thickness 1.9 and 1.2%, for the control and trained leg, respectively). Moreover, V wave and H reflex did not change significantly in all the groups studied (Vwave/M wave ratio -7.9 and -2.6%, and H max/M max ratio -3.8 and -4%, for the control and trained leg, respectively).
Conclusions:
Collectively, the present data suggest that in spite of the changes occurring in soleus strength and thickness, 4 weeks of low-load resistance training, with or without BFR, does not cause any change in neural drive or motoneuronal excitability.
Studies examining resistance training are of importance given that increasing or maintaining muscle mass aids in the prevention or attenuation of chronic disease. Within the literature, it is common practice to administer a set number of target repetitions to be completed by all individuals (i.e. 3 sets of 10) while setting the load relative to each individual?s predetermined strength level (usually a one-repetition maximum). This is done under the assumption that all individuals are receiving a similar stimulus upon completing the protocol, but this does not take into account individual variability with regard to how fatiguing the protocol actually is. Another limitation that exists within the current literature is the reporting of exercise volume in absolute or relative terms that are not truly replicable as they are both load-dependent and will differ based on the number of repetitions individuals can complete at a given relative load. Given that the level of fatigue caused by an exercise protocol is a good indicator of its hypertrophic potential, the most appropriate way to ensure all individuals are given a common stimulus is to prescribe exercise to volitional fatigue. While some authors commonly employ this practice, others still prescribe an arbitrary number of repetitions, which may lead to unfair comparisons between exercise protocols. The purpose of this opinion piece is to provide evidence for the need to standardize studies examining muscle hypertrophy. In our opinion, one way in which this can be accomplished is by prescribing all sets to volitional fatigue.
Purpose:
Applying blood flow restriction during low-load resistance training has been shown to augment muscle hypertrophy which has been attributed to metabolic accumulation. It remains unknown, however, whether metabolites can augment muscle growth when maintained post-exercise.
Methods:
Thirteen untrained individuals (6 males and 7 females) performed 24 training sessions. The control arm performed one set of elbow flexion (70 % 1RM) to volitional fatigue, while the experimental arm performed the same protocol immediately followed by 3 min of blood flow restriction (70 % arterial occlusion). Muscle growth (ultrasound) was measured at 50, 60, and 70 % of the distance between the lateral epicondyle and acromion process.
Results:
Both conditions completed the same exercise volume [3678 (95 % CI 2962, 4393) vs. 3638 kg (95 % CI 2854, 4423)]. There was a condition by time interaction (p = 0.031) demonstrating an attenuation of muscle growth at the 60 % site in the experimental [pre 3.1 (95 % CI 2.8, 3.5), post 3.1 (95 % CI 2.7, 3.5) cm] vs. control [pre 3.1 (95 % CI 2.6, 3.6), post 3.3 (95 % CI 2.8, 3.7) cm] condition. Muscle growth at the 50 % and 70 % sites was similar at the group level, although there were attenuations at the individual level. Exploratory analyses of pre-post mean (95 % CI) changes in muscle thickness suggested that this attenuation in the experimental condition occurred only in females [50 % site 0.0 (-0.2, 0.0) cm; 60 % site -0.1 (-0.3, 0.0) cm; 70 % site 0.0 (-0.1, 0.1) cm].
Conclusions:
The application of blood flow restriction post high-load training did not augment muscle growth for either sex, and appeared to attenuate muscle growth among females.
The purpose of this study was to examine the acute skeletal muscle and perceptual responses to blood flow restriction (BFR) exercise to failure between narrow nylon and elastic inflatable cuffs at rest and during exercise. Torque and muscle thickness was measured pre, post, and 5, 20, 40, and 60 min post-exercise with muscle activation being measured throughout exercise. Resting arterial occlusion pressure was different between the nylon [139 (14) mmHg] and elastic [246 (71) mmHg, p < 0.001] cuffs. However, when exercising at 40 % of each cuff’s respective arterial occlusion pressure [nylon: 57 (7) vs. elastic: 106 (38) mmHg, p < 0.001], there were no differences in repetitions to failure, torque, muscle thickness, or muscle activation between the cuffs. Exercising with cuffs of different material but similar width resulted in the same acute muscular response when the cuffs were inflated to a pressure relative to each individual cuff.
Purpose:
To examine the effects of neuromuscular electrical stimulation (NMES) and blood flow restricted (BFR) exercise on wrist extensors cross-sectional area (CSA), torque and hand functions compared NMES only in individuals with incomplete tetraplegia. The acute effect of an acute bout of NMES with BFR on flow mediated dilation (FMD) was compared with BFR only.
Method:
Nine men completed 6 weeks twice weekly of bilateral NMES training of the wrist extensor muscles. The right forearm received NMES + BFR (30 % above the resting systolic blood pressure), while the left forearm received NMES only. The CSA of the extensor carpi radialis longus (ECRL) and extensor digitorum communis (EDC) muscles was measured on ultrasound images. Torque was measured isometrically and hand function with grasp and release test. Another eight men with SCI received NMES+BFR to the right forearm, while the left forearm received BFR only. Immediately, the FMD of the brachial artery was measured.
Result:
Following training, the ECRL CSA was 17 % greater in the NMES+BFR forearm (mean difference = 0.6 cm(2), p = 0.003) compared with the NMES only. The NMES+BFR had a 15 % increase in ECRL CSA (mean increase = 0.58 cm(2), p = 0.048). FMD increased (p = 0.05) in the exercise arm (12 ± 3 %) compared with the control arm (6.5 ± 6 %).
Conclusion:
NMES training with BFR is a strategy that can increase skeletal muscle size. NMES with and without BFR can improve wrist strength and hand function. The acute effects of NMES+BFR may suggest that an increase in FMD may partially contribute to skeletal muscle hypertrophy.
Purpose:
The main aim of this study was to examine differences in upper arm arterial occlusion pressure (AOP) between three different cuff widths and how individual characteristics influence this. Additional aims of the study were to investigate differences in AOP due to sex and race and to create regression equations that estimate AOP for each cuff width.
Methods:
Two hundred and forty nine participants (males n = 102; females n = 147) visited the laboratory once for measurement of arm length, arm circumference, and resting brachial systolic (bSBP) and diastolic blood pressure (bDBP). Next, each cuff was applied to the upper arm and inflated until a Doppler probe placed at the radial artery no longer detected blood flow. The minimum inflation pressure that caused cessation of blood flow was determined to be the AOP.
Results:
Differences in AOP were observed between cuff widths (p < 0.001). The 5-cm-wide cuff required the greatest inflation pressure [145 (19) mmHg], followed by the 10 cm [123 (13) mmHg], and 12-cm-wide cuff [120 (12) mmHg]. A model encompassing arm circumference, bSBP, arm length, bDBP, and sex explained the most variance in AOP for each cuff (5 cm, R (2) = 0.651; 10 cm, R (2) = 0.570; 12 cm, R (2) = 0.557). However, arm circumference explained the most unique variance for each cuff. When separated by sex, males required greater pressures. Additionally, after controlling for sex, it was found that non-Hispanic Blacks required greater pressures compared with Whites. The regression equations for each cuff width are as follows: 5 cm (mmHg) = 2.926 (arm circumference) + 1.002 (bSBP) - 0.428 (arm length) + 0.213 (bDBP) + 12.668 (sex) - 68.493; 10 cm (mmHg) = 1.545 (arm circumference) + 0.722 (bSBP) - 0.235 (arm length) + 0.205 (bDBP) + 6.378 (sex) - 15.918; 12 cm (mmHg) = 1.393 (arm circumference) + 0.710 (bSBP) - 0.294 (arm length) + 0.164 (bDBP) + 6.419 (sex) - 8.752.
Conclusions:
The AOP is dependent upon cuff width, highlighting the need for authors to report cuff width and consider the impact it has on restriction. Participant characteristics, especially arm circumference, should be considered when applying this blood flow restriction pressure. Lastly, both sex and race have an impact on AOP, although it is not presently known how meaningful this difference is.
to the editor: We read with interest the article by Spranger et al. ([7][1]) in which the authors discussed the exercise pressor reflex in response to blood flow restriction (BFR) exercise. Within, the authors cite an impracticality of standardizing cuff pressure due to differences in cuff width,
We used transcranial magnetic stimulation (TMS) to investigate whether an acute bout of resistance exercise with blood flow restriction (BFR) stimulated changes in corticomotor excitability (motor evoked potential, MEP) and short-interval intracortical inhibition (SICI), and compared the responses to two traditional resistance exercise methods. Ten males completed four unilateral elbow flexion exercise trials in a balanced, randomized crossover design: (1) heavy-load (HL: 80% one-repetition maximum [1-RM]); (2) light-load (LL; 20% 1-RM) and two other light-load trials with BFR applied; (3) continuously at 80% resting systolic blood pressure (BFR-C); or (4) intermittently at 130% resting systolic blood pressure (BFR-I). MEP amplitude and SICI were measured using TMS at baseline, and at four time-points over a 60 min post-exercise period. MEP amplitude increased rapidly (within 5 min post-exercise) for BFR-C and remained elevated for 60 min post-exercise compared with all other trials. MEP amplitudes increased for up to 20 and 40 min for LL and BFR-I, respectively. These findings provide evidence that BFR resistance exercise can modulate corticomotor excitability, possibly due to altered sensory feedback via group III and IV afferents. This response may be an acute indication of neuromuscular adaptations that underpin changes in muscle strength following a BFR resistance training programme.
The purpose of this study was to assess the cross education of strength and changes in the underlying mechanisms (muscle size, activation, and hormonal response) following a 4-week unilateral resistance training (URT) program. A group of nine untrained men completed a 4-week URT program on the dominant leg (DOM), while cross education was measured in the non-dominant leg (NON); and were compared to a control group (n=8, CON). Unilateral isometric force (PKF), leg press (LP) and leg extension (LE) strength, muscle size (via ultrasonography) and activation (via electromyography) of the rectus femoris and vastus lateralis, and the hormonal response (testosterone, growth hormone, insulin, and insulin-like growth factor-1) were tested pre- and post-training. Group × time interactions were present for PKF, LP, LE, and muscle size in DOM and for LP in NON. In all interactions, the URT group improved significantly better than CON. There was a significant acute hormonal response to URT, but no chronic adaptation after the 4-week training program. Four weeks of URT resulted in an increase in strength and size of the trained musculature, as well as cross education of strength in the untrained musculature, which may occur without detectable changes in muscle size, activation, or the acute hormonal response.
The present study investigated the effects of acute and chronic eccentric exercise on the hypoxia-inducible factor (HIF)-1α activation response and the concomitant modulation of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) expression in rat skeletal muscle. Twenty-four male Wistar rats were randomly assigned to three experimental groups: rested control group, acutely exercised group after an intermittent downhill protocol for 90 min, and acutely exercise group with a previous eccentric training of 8 wk. HIF-1α activation, VEGF and eNOS gene expression, protein content, and promoter activation were assessed in vastus lateralis muscle biopsies. Acute eccentric exercise induced a marked activation of HIF-1α and resulted in increased VEGF and eNOS mRNA level and protein concentration. The binding of HIF-1α to the VEGF and eNOS promoters, measured by a chromatin immunoprecipitation assay, was undetectable in rested rats, whereas it was evident in acutely exercised animals. Acute exercise also increased myeloperoxidase, toll-like receptor-4, tumor necrosis factor-α, and interleukin-1β protein content, suggesting a contribution of proinflammatory stimuli to HIF-1α activation and VEGF overexpression. All of these effects were partially abolished by training. Moreover, training resulted in an increased capillary density. In summary, our findings indicate that eccentric exercise prompts an HIF-1α response in untrained skeletal muscle that contributes to the upregulation of VEGF and eNOS gene expression and is attenuated after an eccentric training program.
We compared the effects of different protocols of blood-flow restriction training (BFRT) with different occlusion pressures and/or exercise intensities on muscle mass and strength. We also compared BFRT protocols with conventional high-intensity resistance training (RT).
Twenty-six subjects had each leg allocated to two of five protocols. BFRT protocols were performed at either 20 or 40 % 1-RM with either 40 or 80 % occlusion pressure: BFRT20/40, BFRT20/80, BFRT40/40, and BFRT40/80. Conventional RT was performed at 80 % 1-RM (RT80) without blood-flow restriction. Maximum dynamic strength (1-RM) and quadriceps cross-sectional area (CSA) were assessed at baseline and after 12 weeks.
Regarding muscle mass, increasing occlusion pressure was effective only at very low intensity (BFRT20/40 0.78 % vs. BFRT20/80 3.22 %). No additional increase was observed at higher intensities (BFRT40/40 4.45 % vs. BFRT40/80 5.30 %), with no difference between the latter protocols and RT80 (5.90 %). Exercise intensity played a role in CSA when comparing groups with similar occlusion pressure. Muscle strength was similarly increased among BFRT groups (~12.10 %) but to a lesser extent than RT80 (21.60 %).
In conclusion, BFRT protocols benefit from higher occlusion pressure (80 %) when exercising at very low intensities. Conversely, occlusion pressure seems secondary to exercise intensity in more intense (40 % 1-RM) BFRT protocols. Finally, when considering muscle strength, BFRT protocols seem less effective than high-intensity RT.
Blood flow restriction (BFR) training (also known as Kaatsu training) is an increasingly common practice employed during resistance exercise by athletes attempting to enhance skeletal muscle mass and strength. During BFR training, blood flow to the exercising muscle is mechanically restricted by placing flexible pressurizing cuffs around the active limb proximal to the working muscle. This maneuver results in the accumulation of metabolites (e.g., protons, lactic acid) in the muscle interstitium that increase muscle force and promote muscle growth. Therefore, the premise of BFR training is to simulate and receive the benefits of high-intensity resistance exercise while merely performing low-intensity resistance exercise. This technique has also been purported to provide health benefits to the elderly, individuals recovering from joint injuries and cardiac rehabilitation patients. Since the seminal work of Alam and Smirk in the 1930s, it has been well established that reductions in blood flow to exercising muscle engage the exercise pressor reflex (EPR), a reflex that significantly contributes to the autonomic cardiovascular response to exercise. However, the EPR and its likely contribution to the BFR-mediated cardiovascular response to exercise is glaringly missing from the scientific literature. Inasmuch as the EPR has been shown to generate exaggerated increases in sympathetic nerve activity in disease states such as hypertension (HTN), heart failure (HF) and peripheral artery disease (PAD), concerns are raised that BFR training can be used safely for the rehabilitation of patients with cardiovascular disease as has been suggested.
Copyright © 2015, American Journal of Physiology - Heart and Circulatory Physiology.
Limited data exist on the efficacy of low-load blood flow-restricted strength training (BFR), as compared directly to heavy-load strength training (HST). Here, we show that twelve weeks of twice-a-week unilateral BFR (30% of 1RM to exhaustion) and HST (6-10RM) of knee extensors provide similar increases in 1RM knee extension and cross sectional area of distal parts of m. quadriceps femoris in nine untrained women (age 22±1 years). The two protocols resulted in similar acute increases in serum levels of human growth hormone. On the cellular level, twelve weeks of BFR and HST resulted in similar shifts in muscle fiber composition in m. vastus lateralis, evident as increased MyHC2A proportions and decreased MyHC2X proportions. It also resulted in similar changes of the expression of 29 genes involved in skeletal muscle function, measured both in a rested-state following twelve weeks of training and subsequent to singular training sessions. Training had no effect on myonuclei proportions. Of particular interest; i) gross adaptations to BFR and HST were greater in individuals with higher proportions of type 2 fibers, ii) both BFR and HST resulted in ~4-fold increases in the expression of the novel exercise-responsive gene Syndecan-4, and iii) BFR provided lesser hypertrophy than HST in the proximal half of m. quadriceps femoris and also in CSApeak, potentially being a consequent of pressure from the tourniquet utilized to achieve blood flow restriction. In conclusion, BFR and HST of knee extensors resulted in similar adaptations in functional, physiological and cell biological parameters in untrained women.
Copyright © 2014, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology.
Background: A previous study has reported a 50% reduction in disuse atrophy of the quadriceps during the first 14 days after anterior cruciate ligament (ACL) reconstruction. A follow-up trial is needed to confirm these promising results. The present study aims to investigate the effect of an occlusion stimulus on quadriceps atrophy after ACL reconstruction.
Methods: A total of 24 subjects participated in the study. They were randomized into two groups. Starting the 2nd day after surgery, the occlusion group received an occlusion stimulus for 5 min, followed by removal of the occlusive pressure for 3 min. This was repeated five times in one training session, twice daily. During the period of occlusive stimulus, the subjects performed 20 low load exercises for the quadriceps. The control group followed the same exercise protocol, but without the occlusion stimulus. Changes in quadriceps anatomical cross section area (ACSA) were measured using axial magnetic resonance (MR) images at 40% and 50% of the length of the femur.
Results: Both groups had a significant reduction of quadriceps ACSA from 2 days before surgery to 16 days after surgery. During the intervention period, the occlusion group lost 13.8% ± 1.1% (mean ± SEM) and the control group lost 13.1% ± 1.0% of their quadriceps ACSA, respectively. There was no significant difference between the occlusion and control groups with regards to atrophy of the quadriceps muscles.
Conclusion: In conflict with other studies using a similar protocol, application of blood flow restriction the first 14 days after ACL reconstruction did not reduce quadriceps ACSA muscle atrophy measured by MR in a population of athletes.
This study sought to examine the effects of partial vascular occlusion (PVO) on oxidative stress markers in response to resistance exercise and at rest in young resistance-trained males. 12 resistance-trained males performed 6 conditions in random counterbalanced order: rest (R), low-intensity (LIRE: 30% 1RM) and moderate-intensity (MIRE: 70% 1RM) resistance exercise with or without PVO. Blood samples were obtained before and immediately after each condition and plasma protein carbonyls (PC), glutathione ratio, oxygen radical absorbance capacity (ORAC), and xanthine oxidase (XO) were evaluated. The addition of PVO resulted in significantly greater plasma PC and glutathione ratio in the rest condition. During LIRE the addition of PVO significantly attenuated plasma PC. The MIRE condition, independent of PVO, resulted in significantly higher PC concentration and glutathione ratio compared to the rest and LIRE conditions. The addition of PVO during MIRE resulted in a significant increase in PC. Thus, this study revealed that PVO increased oxidative stress at rest and enhanced the oxidative stress response to MIRE, but when combined with LIRE oxidative stress was attenuated. These findings suggest that the utilization of PVO during LIRE may alter ROS-induced accumulation in the blood which may influence cellular signaling.
© Georg Thieme Verlag KG Stuttgart · New York.
The current study investigated the effects of acute and chronic eccentric exercise on the hypoxia-inducible factor (HIF)-1α activation response and the concomitant modulation of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) expression in rat skeletal muscle. Twenty four male Wistar rats were randomly assigned to three experimental groups: rested control group, acutely exercised group after an intermittent downhill protocol for 90 min, and acutely exercise group with a previous eccentric training of 8 wk. HIF-1α activation, and VEGF and eNOS gene expression, protein content, and promoter activation were assessed in vastus lateralis muscle biopsies. Acute eccentric exercise induced a marked activation of HIF-1α and resulted in increased VEGF and eNOS mRNA level and protein concentration. The binding of HIF-1α to the VEGF and eNOS promoters, measured by a chromatin immunoprecipitation assay, was undetectable in rested rats, whereas it was evident in acutely exercised animals. Acute exercise also increased myeloperoxidase (MPO), toll-like receptor(TLR)-4, tumour necrosis factor (TNF)α and interleukin (IL)-1β protein content, suggesting a contribution of pro-inflammatory stimuli to HIF-1α activation and VEGF overexpression. All these effects were partially abolished by training. Moreover, training resulted in an increased capillary density. In summary, our findings indicate that eccentric exercise prompts an HIF-1α response in untrained skeletal muscle which contributes to the up-regulation of VEGF and eNOS gene expression and is attenuated after an eccentric training program.
Copyright © 2014, Journal of Applied Physiology.
This study investigated the hypertrophic potential of load-matched blood-flow restricted resistance training (BFR) vs free-flow traditional resistance training (low-load TRT) performed to fatigue. Ten healthy young subjects performed unilateral BFR and contralateral low-load TRT elbow flexor dumbbell curl with 40% of one repetition maximum until volitional concentric failure 3 days per week for 6 weeks. Prior to and at 3 (post-3) and 10 (post-10) days post-training, magnetic resonance imaging (MRI) was used to estimate elbow flexor muscle volume and muscle water content accumulation through training. Acute changes in muscle thickness following an early vs a late exercise bout were measured with ultrasound to determine muscle swelling during the immediate 0-48 h post-exercise. Total work was threefold lower for BFR compared with low-load TRT (P < 0.001). Both BRF and low-load TRT increased muscle volume by approximately 12% at post-3 and post-10 (P < 0.01) with no changes in MRI-determined water content. Training increased muscle thickness during the immediate 48 h post-exercise (P < 0.001) and to greater extent with BRF (P < 0.05) in the early training phase. In conclusion, BFR and low-load TRT, when performed to fatigue, produce equal muscle hypertrophy, which may partly rely on transient exercise-induced increases in muscle water content.
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
The extent of skeletal muscle hypertrophy in response to resistance training is highly variable in humans. The main objective of this study was to explain the nature of this variability. More specifically, we focused on the myogenic stem cell population, the satellite cell (SC) as a potential mediator of hypertrophy. Twenty-three males (aged 18-35 yrs) participated in 16 wk of progressive, whole body resistance training, resulting in changes of 7.9±1.6% (range of -1.9-24.7%) and 21.0±4.0% (range of -7.0 to 51.7%) in quadriceps volume and myofibre cross-sectional area (CSA), respectively. The SC response to a single bout of resistance exercise (80% 1RM), analyzed via immunofluorescent staining resulted in an expansion of type II fibre associated SC 72 h following exercise (pre: 11.3±0.9; 72 h: 14.8±1.4 SC/type II fibre; p<0.05). Training resulted in an expansion of the SC pool associated with type I (pre: 10.7±1.1; post: 12.1±1.2 SC/type I fibre; p<0.05) and type II fibres (pre: 11.3±0.9; post: 13.0±1.2 SC/type II fibre; p<0.05). Analysis of individual SC responses revealed a correlation between the relative change in type I associated SC 24 to 72 hours following an acute bout of resistance exercise and the percentage increase in quadriceps lean tissue mass assessed by MRI (r2 = 0.566, p = 0.012) and the relative change in type II associated SC following 16 weeks of resistance training and the percentage increase in quadriceps lean tissue mass assessed by MRI (r2 = 0.493, p = 0.027). Our results suggest that the SC response to resistance exercise is related to the extent of muscular hypertrophy induced by training.
High-intensity resistance training (HRT) has been recommended to offset age-related loss in muscle strength and mass. However, part of the elderly population is often unable to exercise at high-intensities. Alternatively, low-intensity resistance training with blood flow restriction (LRT-BFR) has emerged. The purpose of the present study was to compare the effects of LRT-BFR and HRT on quadriceps muscle strength and mass in elderly. Twenty-three elderly individuals, 14 men and nine women (age: 64.04 ± 3.81 years; weight: 72.55 ± 16.52 Kg; height: 163 ± 11cm), undertook 12 weeks of training. Subjects were ranked according to their pre-training quadriceps cross-sectional area (CSA) values and then randomly allocated into one of the following groups: (1) control group (CG); (2) HRT: 4 X 10 repetitions 70-80% 1-RM; (3) LRT-BFR: 4 sets (1 x 30 and 3 x 15 repetitions) 20-30% 1-RM. The occlusion pressure was set at 50% of maximum tibial arterial pressure and sustained during the whole training session. Leg-press 1-RM and quadriceps CSA were evaluated at pre- and post-training. A mixed-model analysis was performed and the significance level was set at P ≤ 0.05. Both training regimes were effective in increasing pre- to post-training leg-press 1-RM (HRT: ∼54 %, P < 0.001; LRT-BFR: ∼17 %, P = 0.067) and quadriceps CSA (HRT: 7.9 %, P < 0.001; LRT-BFR: 6.6 %, P < 0.001), however, HRT seems to induce greater strength gains. In summary, LRT-BFR constitutes an important surrogate approach to HRT as an effective training method to induce gains in muscle strength and mass in elderly.
Restriction of blood flow to a contracting muscle during low-intensity resistance exercise (BFR exercise) stimulates mTORC1 signaling and protein synthesis in human muscle within 3 hours post-exercise. However, there is a lack of mechanistic data to provide a direct link between mTORC1 activation and protein synthesis in human skeletal muscle following BFR exercise. Therefore, the primary purpose of this study was to determine if mTORC1 signaling is necessary for stimulating muscle protein synthesis after BFR exercise. A secondary aim was to describe the 24-hour time-course response in muscle protein synthesis and breakdown following BFR exercise. Sixteen healthy young men were randomized to one of two groups. Both the control group (CON) and rapamycin (RAP) groups completed BFR exercise however, RAP was administered 16mg of the mTOR inhibitor, rapamycin, one hour prior to BFR exercise. BFR exercise consisted of 4 sets of leg extension exercise at 20% of 1RM. Muscle biopsies were collected from the vastus lateralis before exercise and at 3, 6 and 24 hr after BFR exercise. Mixed muscle protein fractional synthetic rate increased by 42% at 3 hr post-exercise and 69% at 24 hr post-exercise in CON whereas this increase was inhibited in the RAP group. Phosphorylation of mTOR (Ser(2448)) and S6K1 (Thr(389)) were also increased in CON but inhibited in RAP. Mixed muscle protein breakdown was not significantly different across time or groups. We conclude that activation of mTORC1 signaling and protein synthesis in human muscle following BFR exercise is inhibited in the presence of rapamycin.
The purpose of this study was to determine whether the acute hormone response to exercise differed between low intensity blood flow restricted resistance exercise and traditional high-intensity resistance exercise in college-aged women. A total of 13 healthy women (aged 18-25 yrs), who were taking oral contraceptives, volunteered for this randomized crossover study. Subjects performed a session of low intensity blood flow restricted resistance exercise (BFR) (20% of 1-RM, 1 set 30 reps, 2 sets 15 reps) and a session of traditional high intensity resistance exercise without blood flow restriction (HI) (3 sets of 10 repetitions at 80% of 1-RM) on separate days. Fasting serum cortisol and growth hormone (GH) and blood lactate responses were measured in the morning pre and post exercise sessions. GH (Change: HI: 6.34 ± 1.72; BFR: 4.22 ± 1.40 ng·mL(-1)) and cortisol (Change: HI: 4.46 ± 1.53; BFR: 8.10 ± 2.30 ug·dL(-1)) significantly (p < 0.05) increased immediately post exercise for both protocols compared to baseline and there were no significant differences between the protocols for these responses. In contrast, blood lactate levels (HI: 7.35 ± 0.45; BFR: 4.02 ± 0.33 mmol·L(-1)) and ratings of perceived exertion were significantly (p < 0.01) higher for the HI protocol. In conclusion, acute BFR restricted resistance exercise stimulated similar increases in anabolic and catabolic hormone responses in young women. Key PointsGrowth hormone and cortisol levels significantly increased after a single bout of low intensity blood flow restricted resistance exercise in young women.There were no significant differences in hormone responses between the low intensity blood flow restricted protocol and the traditional high intensity higher total workload protocol.Low intensity blood flow restricted resistance exercise provides a sufficient stimulus to elicit anabolic and catabolic hormone responses in young women.
The purpose of this study was to examine the effects of a seven-week, practical blood flow restriction (BFR) protocol used in conjunction with a strength training program on measures of muscular strength and size in collegiate American football players. Sixty-two participants were divided into four groups. Three groups completed a traditional upper- and lower-body split strength program. Two of these groups also completed supplemental lifting sessions. Of these two, one completed the additional lifts with blood flow restriction. The final group completed a modified training program, followed by the supplemental lifts, with blood flow restriction. The supplemental lifting protocol consisted of bench press and squat, utilizing 20% 1RM for four sets with 30 repetitions performed in the first set and 20 repetitions performed in the following three. Each set was separated by 45 seconds of rest. The supplemental bench press was completed at the end of upper-body days, and the squat at the end of lower-body days. Dependent measures were taken prior to the start of the program and again upon conclusion: upper- and lower-body girths, 1RM bench and squat. Results of a 4 X 2 mixed model MANCOVA revealed a significant difference for the interaction on the dependent variables. Follow-up univariate ANOVAs indicated a significant difference for 1RM squat. This suggests that a practical BFR program used in addition to a traditional strength training program can be effective at increasing 1RM squat performance. The use of elastic knee wraps makes BFR a feasible training option for coaches and athletes.
Our aim in the current study was to determine the necessity of satellite cells for long-term muscle growth and maintenance. We utilized a transgenic Pax7-DTA mouse model, allowing for the conditional depletion of > 90% of satellite cells with tamoxifen treatment. Synergist ablation surgery, where removal of synergist muscles places functional overload on the plantaris, was used to stimulate robust hypertrophy. Following 8 wk of overload, satellite cell-depleted muscle demonstrated an accumulation of extracellular matrix (ECM) and fibroblast expansion that resulted in reduced specific force of the plantaris. Although the early growth response was normal, an attenuation of hypertrophy measured by both muscle wet weight and fiber cross-sectional area occurred in satellite cell-depleted muscle. Isolated primary myogenic progenitor cells (MPCs) negatively regulated fibroblast ECM mRNA expression in vitro, suggesting a novel role for activated satellite cells/MPCs in muscle adaptation. These results provide evidence that satellite cells regulate the muscle environment during growth.-Fry, C. S., Lee, J. D., Jackson, J. R., Kirby, T. J., Stasko, S. A., Liu, H., Dupont-Versteegden, E. E., McCarthy, J. J., Peterson, C. A. Regulation of the muscle fiber microenvironment by activated satellite cells during hypertrophy.
We examined the effect of walk training combined with blood flow restriction (BFR) on the size of blood flow-restricted distal muscles, as well as, on the size of non-restricted muscles in the proximal limb and trunk. Nine men performed walk training with BFR and 8 men performed walk training alone. Training was conducted two times a day, 6 days/wk, for 3 wk using five sets of 2-min bouts (treadmill speed at 50 m/min), with a 1-min rest between bouts. After walk training with BFR, MRI-measured upper (3.8%, P < 0.05) and lower leg (3.2%, P < 0. 05) muscle volume increased significantly, whereas the muscle volume of the gluteus maximus (-0.6%) and iliopsoas (1.8%) and the muscle CSA of the lumber L4-L5 (-1.0) did not change. There was no significant change in muscle volume in the walk training alone. Our results suggest that the combination of leg muscle blood flow restriction with slow walk training elicits hypertrophy only in the distal blood flow restricted leg muscles. Exercise intensity may be too low during BFR walk training to increase muscle mass in the non- blood flow restricted muscles (gluteus maximus and other trunk muscles). Key pointsPrevious studies of blood flow restricted walk training have focused solely on thigh muscles distal to pressure cuffs placed on the upper most portion of the proximal thigh.In the current study, both proximal and distal muscles were evaluated following the combination of walk training with leg blood flow restriction (BFR). Muscle hypertrophy only occurred in the thigh and lower leg, which were the blood flow restricted muscles examined.No significant change was observed in the non-restricted trunk muscles following 3 weeks of twice-daily BFR walk training.
Concurrent improvements in aerobic capacity and muscle hypertrophy in response to a single mode of training have not been reported. We examined the effects of low-intensity cycle exercise training with and without blood flow restriction (BFR) on muscle size and maximum oxygen uptake (VO2max). A group of 19 young men (mean age ± SD: 23.0 ± 1.7 years) were allocated randomly into either a BFR-training group (n=9, BFR-training) or a non-BFR control training group (n=10, CON-training), both of which trained 3 days/wk for 8 wk. Training intensity and duration were 40% of VO2max and 15 min for the BFR-training group and 40% of VO2max and 45 min for the CON-training group. MRI-measured thigh and quadriceps muscle cross-sectional area and muscle volume increased by 3.4-5.1% (P < 0.01) and isometric knee extension strength tended to increase by 7.7% (p < 0.10) in the BFR-training group. There was no change in muscle size (~0.6%) and strength (~1.4%) in the CON-training group. Significant improvements in VO2max (6.4%) and exercise time until exhaustion (15.4%) were observed in the BFR-training group (p < 0.05) but not in the CON-training group (-0.1 and 3. 9%, respectively). The results suggest that low-intensity, short-duration cycling exercise combined with BFR improves both muscle hypertrophy and aerobic capacity concurrently in young men. Key pointsConcurrent improvements in aerobic capacity and muscle hypertrophy in response to a single mode of training have not been reported.In the present study, low-intensity (40% of VO2max) cycle training with BFR can elicit concurrent improvement in muscle hypertrophy and aerobic capacity.
Blood flow restriction (BFR) alone or in combination with exercise has been shown to result in favorable effects on skeletal muscle function and morphology (Loenneke et al., 2012a). BFR is a stimulus commonly applied with specialized pressure cuffs placed at the top of a limb which are inflated to a set pressure throughout exercise. The pressure applied should be high enough to occlude venous return from the muscle but low enough to maintain arterial inflow into the muscle. Throughout the literature several different methods are applied with respect to setting the BFR pressure, however, many of these appear methodologically flawed. The purpose of the current manuscript is to discuss the importance of setting BFR cuff pressure based on appropriate factors. This manuscript will focus on applying pressures to the lower limbs because the majority of the data has been collected on the lower body.
It is well established that regimented resistance training can promote increases in muscle hypertrophy. The prevailing body of research indicates that mechanical stress is the primary impetus for this adaptive response and studies show that mechanical stress alone can initiate anabolic signalling. Given the dominant role of mechanical stress in muscle growth, the question arises as to whether other factors may enhance the post-exercise hypertrophic response. Several researchers have proposed that exercise-induced metabolic stress may in fact confer such an anabolic effect and some have even suggested that metabolite accumulation may be more important than high force development in optimizing muscle growth. Metabolic stress pursuant to traditional resistance training manifests as a result of exercise that relies on anaerobic glycolysis for adenosine triphosphate production. This, in turn, causes the subsequent accumulation of metabolites, particularly lactate and H(+). Acute muscle hypoxia associated with such training methods may further heighten metabolic buildup. Therefore, the purpose of this paper will be to review the emerging body of research suggesting a role for exercise-induced metabolic stress in maximizing muscle development and present insights as to the potential mechanisms by which these hypertrophic adaptations may occur. These mechanisms include increased fibre recruitment, elevated systemic hormonal production, alterations in local myokines, heightened production of reactive oxygen species and cell swelling. Recommendations are provided for potential areas of future research on the subject.
Muscle fatigue is the decline in performance of muscles observed during periods of intense activity. ATP consumption exceeds production during intense activity and there are multiple changes in intracellular metabolites which may contribute to the changes in crossbridge activity. It is also well-established that a reduction in activation, either through action potential changes or reduction in Ca²⁺ release from the sarcoplasmic reticulum (SR), makes an additional contribution to fatigue. In this review we focus on the role of intracellular inorganic phosphate (Pi) whose concentration can increase rapidly from around 5–30 mM during intense fatigue. Studies from skinned muscle fibers show that these changes substantially impair myofibrillar performance although the effects are strongly temperature dependent. Increased Pi can also cause reduced Ca²⁺ release from the SR and may therefore contribute to the reduced activation. In a recent study, we have measured both Pi and Ca²⁺ release in a blood-perfused mammalian preparation and the results from this preparation allows us to test the extent to which the combined effects of Pi and Ca²⁺ changes may contribute to fatigue.
Purpose:
To determine if muscle growth is important for increasing muscle strength or if changes in strength can be entirely explained from practicing the strength test.
Methods:
Thirty-eight untrained individuals performed knee extension and chest press exercise for 8 weeks. Individuals were randomly assigned to either a high-volume training group (HYPER) or a group just performing the one repetition maximum (1RM) strength test (TEST). The HYPER group performed 4 sets to volitional failure (~8-12RM) while the TEST group performed up to 5 attempts to lift as much weight as possible one time each visit.
Results:
Data are presented as mean (90% CI). The change in muscle size was greater in the HYPER group for both the upper and lower body at most but not all sites. The change in 1RM strength for both the upper [difference of -1.1 (-4.8, 2.4) kg] and lower body [difference of 1.0 (-0.7, 2.8) kg for dominant leg] was not different between groups (similar for non-dominant). Changes in isometric and isokinetic torque were not different between groups. The HYPER group observed a greater change in muscular endurance [difference of 2 (1, 4) repetitions] only in the dominant leg. There were no differences in the change between groups in upper body endurance. There were between group differences for exercise volume [mean (95% CI)] of the dominant [difference of 11049.3 (9254.6, 12844.0) kg] leg (similar for non-dominant) and chest press with the HYPER group completing significantly more total volume [difference of 13259.9 (9632.0, 16887.8) kg].
Conclusion:
These findings suggests that exercise volume nor the change in muscle size from training contributed to greater strength gains compared to just practicing the test.
Recent studies have investigated relative pressures that are applied during blood flow restriction exercise ranging from 40%-90% of resting arterial occlusion pressure; however, no studies have investigated relative pressures below 40% arterial occlusion pressure. The purpose of this study was to characterize the cardiovascular and perceptual responses to different levels of pressures. Twenty-six resistance trained participants performed four sets of unilateral elbow flexion exercise using 30% of their 1RM in combination with blood flow restriction inflated to one of six relative applied pressures (0%, 10%, 20%, 30%, 50%, 90% arterial occlusion pressure). Arterial occlusion pressure was measured before (pre) and immediately after the last set of exercise at the radial artery. RPE and discomfort were taken prior to (pre) and following each set of exercise. Data presented as mean (95% CI) except for perceptual responses represented as the median (25th, 75th percentile). Arterial occlusion pressure increased from pre to post (p<0.001) in all conditions but was augmented further with higher pressures [e.g. 0%: 36 (30-42) mmHg vs. 10%: 39 (34-44) mmHg vs. 90% 46 (41-52) mmHg]. For RPE and discomfort, there were significant differences across conditions for all sets of exercise (p<0.01) with the ratings of RPE [e.g. 0%: 14.5 (13, 17) vs. 10%: 13.5 (12, 17) vs. 90%: 17 (14.75, 19) during last set] and discomfort [e.g. 0%: 3.5 (1.5, 6.25) vs. 10%: 3 (1, 6) vs. 90%: 7 (4.5, 9) during last set] generally being greater at the higher restriction pressures. All of these differences at the higher restriction pressures occurred despite completing a lower total volume of exercise. Applying higher relative pressures results in the greatest cardiovascular response, higher perceptual ratings, and greater decrease in exercise volume compared to lower restriction pressures. Therefore, the perceptual responses from lower relative pressures may be more appealing and provide a safer and more tolerable stimulus for individuals.
Introduction:
Large increases in 1-repetition maximum (1RM) strength have been demonstrated from repeated testing, but it is unknown whether these increases can be augmented by resistance training.
Methods:
Five trained individuals performed a 1RM test and maximal voluntary isometric contraction (MVC) for unilateral elbow flexion exercise on 1 arm (testing arm), while the other arm performed a 1RM test and MVC, in addition to 3 sets of exercise (70% 1RM) (training arm) for 21 straight days.
Results:
Although only the training arm had increased muscle thickness [mean: 0.28 (95% confidence interval: 0.22 - 0.33)] cm, 1RM strength increased similarly in the training [2.2 (95% confidence interval: 0.9 - 3.4) kg; P=0.008] and testing [1.9 (95% confidence interval: 0.5 - 3.2) kg; P=0.019] arms.
Discussion:
Increases in 1RM strength from resistance training are related to the specificity of exercise and are likely driven by mechanisms other than muscle growth. This article is protected by copyright. All rights reserved.
Blood flow restriction (BFR) under low-intensity resistance training (LIRT) can produce similar effects upon muscles to that of high-intensity resistance training (HIRT) while overcoming many of the restrictions to HIRT that occurs in a clinical setting. However, the potential molecular mechanisms of BFR induced muscle hypertrophy remain largely unknown. Here, using a BFR rat model, we aim to better elucidate the mechanisms regulating muscle hypertrophy as induced by BFR and reveal possible clinical therapeutic targets for atrophy cases. We performed genome wide screening with microarray analysis to identify unique differentially expressed genes during rat muscle hypertrophy. We then successfully separated the differentially expressed genes from BRF treated soleus samples by comparing the Affymetrix rat Genome U34 2.0 array with the control. Using qRT-PCR and immunohistochemistry (IHC) we also analyzed other related differentially expressed genes. Results suggested that muscle hypertrophy induced by BFR is essentially regulated by the rate of protein turnover. Specifically, PI3K/AKT and MAPK pathways act as positive regulators in controlling protein synthesis where ubiquitin-proteasome acts as a negative regulator. This represents the first general genome wide level investigation of the gene expression profile in the rat soleus after BFR treatment. This may aid our understanding of the molecular mechanisms regulating and controlling muscle hypertrophy and provide support to the BFR strategies aiming to prevent muscle atrophy in a clinical setting.
Skeletal muscle is a plastic organ that adapts its mass to various stresses by affecting pathways that regulate protein synthesis and degradation. This study investigated the effects of repetitive restriction of muscle blood flow (RRMBF) on microvascular oxygen pressure (PmvO2), mammalian target of rapamycin (mTOR) signaling pathways, and transcripts associated with proteolysis in rat skeletal muscle. Eleven-week-old male Wistar rats under anesthesia underwent six RRMBF consisting of an external compressive force of 100 mmHg for 5 min applied to the proximal portion of the right thigh, each followed by 3 min rest. During RRMBF, PmvO2 was measured by phosphorescence quenching techniques. The total RNA and protein of the tibialis anterior muscle were obtained from control rats, and rats treated with RRMBF 0–6 h after the stimuli. The protein expression and phosphorylation of various signaling proteins were determined by western blotting. The mRNA expression level was measured by real-time RT-PCR analysis. The total muscle weight increased in rats 0 h after RRMBF, but not in rats 1–6 h. During RRMBF, PmvO2 significantly decreased (36.1 ± 5.7 to 5.9 ± 1.7 torr), and recovered at rest period. RRMBF significantly increased phosphorylation of p70 S6-kinase (p70S6k), a downstream target of mTOR, and ribosomal protein S6 1 h after the stimuli. The protein level of REDD1 and phosphorylation of AMPK and MAPKs did not change. The mRNA expression levels of FOXO3a, MuRF-1, and myostatin were not significantly altered. These results suggested that RRMBF significantly decreased PmvO2, and enhanced mTOR signaling pathways in skeletal muscle using a rat model, which may play a role in diminishing muscle atrophy under various conditions in human studies.
Introduction:
We tested the hypothesis that whole body vibration (WBV) is insufficient to expand satellite cell (SC) numbers 24 h post exercise, whereas WBV in combination with blood flow restriction (BFR) is.
Methods:
Twenty-five young men were randomly assigned to one of three groups: WBV, BFR exercise or WBVBFR. SC numbers were determined from muscle biopsies of the vastus lateralis using immunohistochemistry.
Results:
SC quantity and frequency (+99.38%, P = 0.012 and +77.1%, P = 0.010, respectively) only increased in the WBVBFR group. Similar results were obtained for the quantity and frequency of myogenin+ myonuclei (+139.0%, P < 0.001 and +148.4%, P < 0.001, respectively).
Conclusion:
We conclude that modification of WBV by superimposing BFR induced activation and differentiation of SC in young men, all of which had not been observed with WBV or BFR alone. These data suggest that WBVBFR might represent a novel viable anabolic stimulus. This article is protected by copyright. All rights reserved.
Low-load exercise can increase serum hormones such as growth hormone (GH) concentration in young adults when combined with blood flow restriction (BFR), but it is unclear whether walking with BFR (BFR-walk) can elevate them for older adults. Furthermore, it remained untested whether changes in these purported anabolic hormones contribute to BFR-walk-induced muscle hypertrophy. To examine the relationship between the acute and chronic effects of BFR-walk, seven women (age: 64 ± 2 years) performed treadmill walking with (BFR-walk) and without BFR (CON-walk) at 45% of heart rate reserve for 20 min in a randomized crossover design. During BFR-walk, subjects wore 5-cm cuffs on the proximal part of the upper legs. Blood samples were taken before (PRE), immediately after (POST-1) and 15 min post (POST-2) exercise. There was a main effect of time for GH (P<0·01) with levels increasing following exercise. In addition, there was a condition and time main effect for insulin; with insulin increasing to a greater degree with BFR at POST-2. Noradrenaline increased across time for both BFR-walk (P = 0·012) and CON-walk (P<0·001); but BFR-walk induced greater elevations at POST-1 and POST-2. The change in GH, insulin and noradrenaline was not significantly correlated with BFR-walk-induced muscle hypertrophy. These preliminary results suggest that the BFR-walk-induced elevation in the purported anabolic hormones may not have a large impact on muscle growth.
Methods:
Thirty one physically active subjects were assigned to one of three groups: VI [n = 10, 60-70% Heart Rate Reserve (HRR)], LI-BFR (n = 11, 30% HRR with BFR at 160-180 mmHg), and CON (n = 10, no exercise). Subjects in VI and LI-BFR cycled 3 times / week for 6 weeks (total 18 sessions). Body composition, muscle mass, strength, and aerobic capacity were measured pre, post, and after 3 weeks of de-training.
Results:
A group × time interaction (p = 0.019) effect for both knee flexion and leg lean mass were found. For both VI and LI-BFR groups, knee flexion strength was significantly increased between pre and post (p = 0.024, p = 0.01) and between pre and 3 week-post (p=0.039, p = 0.003), respectively. For the LI-BFR group, leg lean mass was significantly increased between pre and 3 week-post (p = 0.024) and between post and 3 week-post (p =0.013). However, there were no significant differences between groups for any variables.
Conclusions:
The LI-BFR elicits an increase in the knee flexion muscle strength over time similar to the VI. An increase in the leg lean mass over time was seen in the LI-BFR, but not in VI and CON.
To investigate the acute and chronic skeletal muscle response to differing levels of blood flow restriction (BFR) pressure.
Fourteen participants completed elbow flexion exercise with pressures from 40% to 90% of arterial occlusion. Pre/Post torque measurements and EMG amplitude of each set were quantified for each condition. This was followed by a separate 8 week training study of the effect of high (90% arterial occlusion) and low (40% arterial occlusion) pressure on muscle size and function.
For the acute study, decreases in torque were similar between pressures [-15.5 (5.9) Nm P=0.344]. For amplitude of the first 3 and last 3 reps there was a time effect. Following training, increases in muscle size (10%), peak isotonic strength (18%), peak isokinetic torque (180 degrees/sec=23%, 60 degrees/sec=11%), and muscular endurance (62%) changed similarly between pressures.
We suggest that higher relative pressures may not be necessary when exercising under BFR. This article is protected by copyright. All rights reserved.
© 2015 Wiley Periodicals, Inc.
Low-load voluntary exercise can induce muscle hypertrophy and strength gain when combined with blood flow restriction (BFR) in working muscles. However, it is unknown whether such hypertrophy and strength gain can be induced by involuntary muscle contractions triggered via low-intensity neuromuscular electrical stimulation (NMES), combined with BFR. The purpose of this article was to investigate whether low-intensity NMES combined with BFR could elicit muscle hypertrophy and strength gain in the quadriceps.
Eight untrained young males (means ± SEs; age 26.2±0.7 years, height 1.74±0.02 m, body weight 71.4±4.8 kg) received 23 min of unilateral low-intensity (5-10% of maximal voluntary contraction) NMES, twice per day, 5 days per week, for 2 weeks, with treatment of one leg being combined with BFR (NMES-BFR) and the other leg receiving NMES alone (NMES-CON). Quadriceps muscle thickness (MT) and isometric and isokinetic strength were measured before and every week throughout the training and detraining periods.
In NMES-BFR legs, MT increased after 2 weeks of training (+3.9%) and decreased after 2 weeks of detraining (-3.0%). NMES-BFR training also increased maximal knee extension strength in isometric (+14.2%) and isokinetic (+7.0% at 90°/s, +8.3% at 180°/s) voluntary contractions. In addition, maximal isometric strength decreased (-6.8%), whereas no large fall (-1.9% at 90°/s, -0.6% at 180°/s) in isokinetic maximal strength was evident after 2 weeks of detraining. In NMES-CON legs, no prominent change was observed; there was a negligible effect on isometric strength.
Low- intensity NMES combined with BFR induces muscle hypertrophy and strength gain in untrained young males.
The purpose of this study was to determine whether arm circumference is predictive of arterial occlusion in the standing position and to determine the change in pressure before and immediately after exercise. Thirty-one participants had their arm circumference, blood pressure and standing arterial occlusion determined before exercise. Participants then completed elbow flexions at 40% of resting arterial occlusion at 30% of their one repetition maximum (1RM). The goal repetitions for the exercise included one set of 30 repetitions followed by 3 sets of 15, with 30s rest between sets. Immediately following the last set, postexercise arterial occlusion was determined. Two different models of hierarchical linear regression were used to determine the greatest predictor of standing arterial occlusion. Our final model explained 69% of the variance in arterial occlusion with arm circumference (β = 0·639, part = 0·568) explaining more than brachial systolic blood pressure (β = 0·312, part = 0·277). Standing arterial occlusion increased from pre- [138 (15) mmHg] to post- [169 (20) mmHg] exercise (P<0·001). In conclusion, the cardiovascular response to blood flow restriction (BFR) in the upper arm following 4 sets of elbow flexion exercise decreases the relative arterial occlusion pressure. In addition, we confirm previous data that circumference explains the most unique variance in arterial occlusion pressure in the upper body. These findings are important as they provide additional insight into making the pressure more uniform between participants throughout exercise.
© 2015 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.
Objective:
Transient receptor potential melastatin-2 (TRPM2) channel is a nonselective cation channel that mediates influx of Ca(2+) and Na(+) with relative permeability of PCa:PNa ≈0.6 in response to cellular oxidative stress. As angiogenesis and ischemic neovascularization are both significantly dependent on oxidant signaling, here we investigated the possible role of vascular endothelial growth factor (VEGF)-induced reactive oxygen species production in activating TRPM2-dependent Ca(2+) signaling and in the mechanism of angiogenesis and ischemic neovascularization.
Approach and results:
We observed that VEGF stimulation rapidly induced the association of TRPM2 and cellular Src kinase with vascular endothelial-cadherin forming a signalplex at vascular endothelial-cadherin junctions in endothelial cells. Using endothelial cells isolated from TRPM2(-/-) mice or after small interfering RNA depletion of TRPM2, we demonstrated that TRPM2-activated Ca(2+) signaling was required for cellular Src kinase-induced phosphorylation of vascular endothelial-cadherin at Y658 and Y731, the crucial sites involved in vascular endothelial-cadherin internalization in response to VEGF. VEGF-induced reactive oxygen species generation activated TRPM2-induced Ca(2+) entry, whereas the reactive oxygen species-insensitive TRPM2 mutant (C1008→A) showed impaired Ca(2+) entry. Endothelial cells depleted of TRPM2 also displayed significantly perturbed migratory phenotype and impaired activation of cellular Src in response to VEGF. TRPM2(-/-) mice reconstituted with wild-type myeloid cells demonstrated aberrant angiogenesis and neovascularization in the hindlimb ischemia model as compared with wild-type mice.
Conclusions:
VEGF-induced angiogenesis and postischemic neovascularization in mice required reactive oxygen species generation in endothelial cells and resultant TRPM2 activation. Thus, our findings provide novel insight into the role of TRPM2 in mechanism of angiogenesis and ischemic neovascularization.
Purpose:
To determine what factors should be accounted for when setting the blood flow restriction (BFR) cuff pressure for the upper and lower body.
Methods:
One hundred and seventy one participants visited the laboratory for one testing session. Arm circumference, muscle (MTH) and fat (FTH) thickness were measured on the upper arm. Next, brachial systolic (SBP) and diastolic (DBP) blood pressure measurements were taken in the supine position. Upper body arterial occlusion was then determined using a Doppler probe. Following this, thigh circumference and lower body arterial occlusion were determined. Models of hierarchical linear regression were used to determine the greatest predictor of arterial occlusion in the upper and lower body. Two models were employed in the upper body, a Field (arm size) and a Laboratory model (arm composition).
Results:
The Laboratory model explained 58 % of the variance in arterial occlusion with SBP (β = 0.512, part = 0.255), MTH (β = 0.363, part = 0.233), and FTH (β = 0.248, part = 0.213) contributing similarly to explained variance. The Field model explained 60 % of the variance in arterial occlusion with arm circumference explaining the greatest amount (β = 0.419, part = 0.314) compared to SBP (β = 0.394, part = 0.266) and DBP (β = 0.147, part = 0.125). For the lower body model the third block explained 49 % of the variance in arterial occlusion with thigh circumference (β = 0.579, part = 0.570) and SBP (β = 0.281, part = 0.231) being significant predictors.
Conclusions:
Our findings indicate that arm circumference and SBP should be taken into account when determining BFR cuff pressures. In addition, we confirmed our previous study that thigh circumference is the greatest predictor of arterial occlusion in the lower body.
Eukaryotic cells coordinately control anabolic and catabolic processes to maintain cell and tissue homeostasis. Mechanistic target of rapamycin complex 1 (mTORC1) promotes nutrient-consuming anabolic processes, such as protein synthesis. Here we show that as well as increasing protein synthesis, mTORC1 activation in mouse and human cells also promotes an increased capacity for protein degradation. Cells with activated mTORC1 exhibited elevated levels of intact and active proteasomes through a global increase in the expression of genes encoding proteasome subunits. The increase in proteasome gene expression, cellular proteasome content, and rates of protein turnover downstream of mTORC1 were all dependent on induction of the transcription factor nuclear factor erythroid-derived 2-related factor 1 (NRF1; also known as NFE2L1). Genetic activation of mTORC1 through loss of the tuberous sclerosis complex tumour suppressors, TSC1 or TSC2, or physiological activation of mTORC1 in response to growth factors or feeding resulted in increased NRF1 expression in cells and tissues. We find that this NRF1-dependent elevation in proteasome levels serves to increase the intracellular pool of amino acids, which thereby influences rates of new protein synthesis. Therefore, mTORC1 signalling increases the efficiency of proteasome-mediated protein degradation for both quality control and as a mechanism to supply substrate for sustained protein synthesis.
The purpose of this study was to determine the muscular adaptations to low-load resistance training performed to fatigue with and without blood flow restriction (BFR). Middle-aged (42–62 years) men (n = 12) and women (n = 6) completed 18 sessions of unilateral knee extensor resistance training to volitional fatigue over 6 weeks. One limb trained under BFR, and the contralateral limb trained without BFR [free flow (FF)]. Before and after the training, measures of anterior and lateral quadriceps muscle thickness (MTh), strength, power and endurance were assessed on each limb. The total exercise training volume was significantly greater for the FF limb compared with the BFR limb (P<0·001). Anterior quadriceps thickness and muscle function increased following the training in each limb with no differences between limbs. Lateral quadriceps MTh increased significantly more (P<0·05) in the limb trained under BFR (BFR: 3·50 ± 0·61 to 3·67 ± 0·62 cm; FF: 3·49 ± 0·73 to 3·56 ± 0·70 cm). Low-load resistance training to volitional fatigue both with and without BFR is viable options for improving muscle function in middle-aged individuals. However, BFR enhanced the hypertrophic effect of low-load training and reduced the volume of exercise needed to elicit increases in muscle function.
Blood flow restricted resistance exercise improves muscle strength; however, the cardiovascular response is not well understood.
This investigation measured local vascular responses, tissue oxygen saturation (StO2), and cardiovascular responses during supine unilateral leg press and heel raise exercise in four conditions: high load with no occlusion cuff (HL), low load with no occlusion cuff (LL), and low load with occlusion cuff pressure set at 1.3 times resting diastolic blood pressure (BFRDBP) or at 1.3 times resting systolic blood pressure (BFRSBP).
Subjects (N=13) (men/women 5/8, 31.8±12.5 yr, 68.3±12.1 kg, mean±SD) performed 3 sets of leg press and heel raise to fatigue with 90-s rest. Artery diameter, velocity time integral (VTI), and stroke volume (SV) were measured using two-dimensional and Doppler ultrasound at rest and immediately after exercise. Heart rate (HR) was monitored using a 3-lead ECG. Finger blood pressure (BP) was acquired by photoplethysmography. Vastus lateralis StO2 was measured using near-infrared spectroscopy (NIRS). A repeated-measures ANOVA was used to analyze exercise work and StO2. Multi-level modeling was used to evaluate the effect of exercise condition on vascular and cardiovascular variables. Statistical significance was set a priori at P<0.05.
Artery diameter did not change from baseline during any of the exercise conditions. Blood flow increased after exercise in each condition except BFRSBP. StO2 decreased during exercise and recovered to baseline levels during rest only in LL and HL. HR, SV, and cardiac output (Q) responses to exercise were blunted in BFR. BP was elevated during rest intervals in BFR.
Our results demonstrate that cuff pressure alters the hemodynamic responses to resistance exercise. These findings warrant further evaluations in individuals presenting cardiovascular risk factors.
Resistance training in combination with practical blood flow restriction (pBFR) is thought to stimulate muscle hypertrophy by increasing muscle activation and muscle swelling. Most previous studies used the KAATSU device; however, little long-term research has been completed using pBFR.
To investigate the effects of pBFR on muscle hypertrophy.
Twenty college-aged male participants with a minimum of 1 year of resistance training experience were recruited for this study. Our study consisted of a randomized, crossover protocol consisting of individuals either using pBFR for the elbow flexors during the first 4 weeks (BFR-HI) or the second 4 weeks (HI-BFR) of an 8-week resistance training programme. Direct ultrasound-determined bicep muscle thickness was assessed collectively at baseline and at the end of weeks 4 and 8.
There were no differences in muscle thickness between groups at baseline (P = 0·52). There were time (P<0·01, ES = 0·99) but no condition by time effects (P = 0·58, ES = 0·80) for muscle thickness in which the combined values of both groups increased on average from week 0 (3·66 ± 0·06) to week 4 (3·95 ± 0·05) to week 8 (4·11 ± 0·07). However, both the BFR-HI and HI-BFR increased significantly from baseline to week 4 (6·9% and 8·6%, P<0·01) and from weeks 4 to 8 (4·1%, 4·0%, P<0·01), respectively.
The results of this study suggest that pBFR can stimulate muscle hypertrophy to the same degree to that of high-intensity resistance training.
The impact of disuse on the loss of skeletal muscle mass and strength has been well documented. Given that most studies have investigated muscle atrophy after more than 2 weeks of disuse, few data are available on the impact of shorter periods of disuse. We assessed the impact of 5 and 14 days of disuse on skeletal muscle mass, strength and associated intramuscular molecular signaling responses.
Twenty-four healthy, young (23±1 y) males were subjected to either 5 (n=12) or 14 (n=12) days of one-legged knee immobilization using a full leg cast. Before and immediately after the immobilization period, quadriceps muscle cross-sectional area (CSA), leg lean mass and muscle strength were assessed, and biopsies were collected from the vastus lateralis.
Quadriceps muscle CSA declined from baseline by 3.5±0.5 (P<0.0001) and 8.4±2.8% (P<0.0001), leg lean mass was reduced by 1.4±0.7 (P=0.07) and 3.1±0.7% (P<0.01), and strength decreased by 9.0±2.3 (P<0.0001) and 22.9±2.6% (P<0.0001) following 5 and 14 days of immobilization, respectively. Muscle myostatin mRNA expression doubled following immobilization (P<0.05) in both groups, while the myostatin precursor isoform protein content decreased after 14 days only (P<0.05). Muscle MAFBx mRNA expression increased from baseline by a similar magnitude following either 5 or 14 days of disuse, whereas MuRF1 mRNA expression had increased significantly only after 5 days.
We conclude that even short periods of muscle disuse can cause substantial loss of skeletal muscle mass and strength, and are accompanied by an early catabolic molecular signaling response. This article is protected by copyright. All rights reserved.
The purpose of this study was to investigate age-related differences in short-term training adaptations in cortical excitability and inhibition. Thirty young (21.9 ± 3.1 years) and 30 older (72.9 ± 4.6 years) individuals participated in the study. Each participant was randomly assigned to a control (n = 30) or a resistance training (n = 30) group, with equal numbers of young and older subjects in each group. Participants completed 2 days of testing, separated by 2 weeks during which time the training group participated in resistance training of the ankle dorsiflexor muscles three times per week. During each testing session, transcranial magnetic stimulation was used to generate motor evoked potentials (MEPs) and silent periods in the tibialis anterior. Hoffmann reflexes (H-reflexes) and compound muscle action potentials (M-waves) were also evoked via electrical stimulation of the peroneal nerve. At baseline, young subjects had higher maximum voluntary contraction (MVC) force (p = 0.002), larger M-wave amplitude (p < 0.001), and longer duration silent periods (p = 0.01) than older individuals, with no differences in the maximal amplitude of the MEP (p = 0.23) or H-reflex (p = 0.57). In the trained group, MVC increased in both young (17.4 %) and older (19.8 %) participants (p < 0.001), and the duration of the silent period decreased by ~15 and 12 ms, respectively (p < 0.001). Training did not significantly impact MEP (p = 0.69) or H-reflex amplitudes (p = 0.38). There were no significant changes in any measures in the control group (p ≥ 0.19) across the two testing sessions. These results indicate that a reduction in cortical inhibition may be an important neural adaptation in response to training in both young and older adults.
Muscle protein synthesis rates decrease during contraction/exercise, but rapidly increase post-exercise. Previous studies mainly focused on signaling pathways that control protein synthesis during post-exercise recovery, such as mTOR and its downstream targets S6K1 and 4E-BP1. In this study, we investigated the effect of high-frequency electrical stimulation on the phosphorylation state of signaling components controling protein synthesis in rat skeletal muscle. Electrical stimulation increased S6K1 Thr389 phosphorylation, which was unaffected by Torin1, a selective mTOR inhibitor, suggesting that S6K1 phosphorylation by contraction was mTOR-independent. Phosphorylation of eIF4B Ser422 was also increased during electrical stimulation, which was abrogated by inhibition of MEK/ERK/RSK1 signaling. Moreover, although phosphorylation of conventional mTOR sites in 4E-BP1 decreased during contraction, mTOR-independent phosphorylation was also apparent, which was associated with the release of 4E-BP1 from eIF4E. The results indicate mTOR-independent phosphorylation of S6K1 and 4E-BP1 and suggest MEK/ERK/RSK1-dependent phosphorylation of eIF4B during skeletal muscle contraction. These phosphorylation events would keep the translation initiation machinery "primed" in an active state so that protein synthesis could quickly resume post-exercise.
Blood flow restriction (BFR) by itself or in combination with exercise has been shown to be beneficial for skeletal muscle. Despite most of the literature showing positive effects of BFR on skeletal muscle, not all studies show a benefit of BFR exercise compared with exercise without BFR. Some of the discrepancy can be explained by differences in methodology. For example, wide (13·5 cm) nylon cuffs result in arterial occlusion at a much lower pressure than narrow elastic (5 cm) cuffs. However, although it is evident that there are differences between elastic narrow (5 cm) cuffs and nylon wide (13·5 cm) cuffs, it is presently unclear whether or not there are differences between two cuffs of similar size (5 cm) but different material (nylon versus elastic). We hypothesized that although the cuffs are of similar size, there would be significant differences in arterial occlusion between two cuff materials. With the participants supine, in a randomized order, either the nylon (5 × 83 cm) or elastic (5 × 135 cm) cuffs were applied to the most proximal portion of each leg. Arterial blood flow was detected using a hand-held bidirectional Doppler probe placed on the posterior tibial artery. A paired sample t-test found no difference between cuff types for arterial occlusion pressure. In conclusion, arterial occlusion pressure is not different between two cuffs of a similar size but different material. This suggests that either elastic or nylon cuffs of the same width should restrict blood flow similarly at the same pressure during resting conditions.
Elastic band (EB) training is a common form of resistance training used by the elderly, individuals with joint problems or those recovering from injury. EB training performed at low intensities by these populations may have little effect on muscle hypertrophy. However, when combined with blood flow restriction (BFR), low-intensity EB resistance training may result in muscle hypertrophy.
Postmenopausal women (61 ± 5 years) were assigned to a moderate-to-high-intensity EB group (MH, n = 8) or a low-intensity EB group combined with BFR (LI-BFR, n = 6). Each group performed seated chest press, seated row and seated shoulder press with EB three times a week for eight weeks. EB colours progressed in each group by having participants maintain a rating of 7–9 on the OMNI Resistance for active muscle (OMNI-RES AM) scale (0–10) throughout training. In the LI-BFR group, BFR pressure progressed during the first 4 weeks of training (80–120 mmHg), after which EB colours were progressed.
1-repetition maximum increased for chest press (P = 0·01), shoulder press (P = 0·02) and seated row (P = 0·01), but no differences were found between groups. Only pectoralis major muscle thickness in the upper body increased (P = 0·04). A trend was found for an increase in total bone-free lean body mass (P = 0·055).
The main findings of this study were that moderate-to-high-intensity EB training and low-intensity EB training with BFR resulted in similar increases in strength, total bone-free lean body mass and muscle thickness.