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Muscle fibre activation and fatigue with low‐load blood flow restricted resistance exercise – An integrative physiology review
Abstract
Blood flow restricted resistance exercise (BFRRE) has been shown to induce increases in muscle size and strength, and continues to generate interest from both clinical and basic research points of view. The low loads employed, typically 20‐50% of the one repetition maximum (1RM), make BFRRE an attractive training modality for individuals who may not tolerate high musculoskeletal forces (e.g. selected clinical patient groups such as frail old adults and patients recovering from sports injury) and/or for highly trained athletes who have reached a plateau in muscle mass and strength.
It has been proposed that achieving a high degree of muscle fibre recruitment is important for inducing muscle hypertrophy with BFRRE, and the available evidence suggest that fatiguing low‐load exercise during ischemic conditions can recruit both slow (type I) and fast (type II) muscle fibres. Nevertheless, closer scrutiny reveals that type II fibre activation in BFRRE has to date largely been inferred using indirect methods such as electromyography (EMG) and magnetic resonance spectroscopy (MRS), while only rarely addressed using more direct methods such as measurements of glycogen stores and phosphocreatine (PCr) levels in muscle fibres. Hence, considerable uncertainity exists about the specific pattern of muscle fiber activation during BFRRE.
Therefore, the purpose of this narrative review was (1) to summarize the evidence on muscle fibre recruitment during BFRRE as revealed by various methods employed for determining muscle fibre usage during exercise, and (2) to discuss reported findings in light of the specific advantages and limitations associated with these methods.
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... Indeed, a robust correlation (r 5 ;0.85) between acute metabolic stress and chronic hypertrophy with ischemic exercise has been reported (39). Conversely, it has been postulated that the anabolic effects of metabolites may simply be achieved through an increased motor unit recruitment and consequently mechanical tension being experienced in a greater number of muscle fibers (43). If such a theory is true, then a threshold of metabolic stress which permits the recruitment of the highest threshold motor units would only be necessary, and any additional metabolite accumulation would not promote proportionally greater adaptations to training. ...
... If such a theory is true, then a threshold of metabolic stress which permits the recruitment of the highest threshold motor units would only be necessary, and any additional metabolite accumulation would not promote proportionally greater adaptations to training. Instead, excessive metabolite accumulation may augment pain and effort signals during exercise by activation of group III/IV afferents (43). In support of this alternative theory, recent evidence indicates that more metabolically demanding BFR protocols (that involve higher volumes of exercise or training to muscular failure) may not necessarily promote greater adaptations, and may instead prolong fatigue and delay subsequent adaptation (5,26,29,34). ...
... Therefore, the combination of exercise loads (30-40% 1RM) and training frequency (3x·wk 21 ) used in this study may have provided a considerable stimulus for these individuals, irrespective of the additional stress imposed by the 2 BFR protocols. Moreover, it may have been that the combination of 30-40% 1RM loads, and the volume of exercise performed each session (2 exercises, 150 repetitions) was sufficient to induce enough peripheral fatigue, even without BFR, to access the highest threshold motor units in some individuals (43). Indeed, Lixandrão et al. (21) observed that when higher loads are used (e.g., 40 vs. 20% 1RM), the influence of cuff pressure (hence, metabolic perturbation to the exercising muscle) on muscle hypertrophy is diminished. ...
Davids, CJ, Raastad, T, James, L, Gajanand, T, Smith, E, Connick, M, McGorm, H, Keating, S, Coombes, JS, Peake, JM, and Roberts, LA. Similar morphological and functional training adaptations occur between continuous and intermittent blood flow restriction. J Strength Cond Res XX(X): 000-000, 2021-The aim of the study was to compare skeletal muscle morphological and functional outcomes after low-load resistance training using 2 differing blood flow restriction (BFR) protocols. Recreationally active men and women (n = 42 [f = 21], 24.4 ± 4.4 years) completed 21 sessions over 7 weeks of load-matched and volume-matched low-load resistance training (30% 1 repetition maximum [1RM]) with either (a) no BFR (CON), (b) continuous BFR (BFR-C, 60% arterial occlusion pressure [AOP]), or (c) intermittent BFR (BFR-I, 60% AOP). Muscle mass was assessed using peripheral quantitative computed tomography before and after training. Muscular strength, endurance, and power were determined before and after training by assessing isokinetic dynamometry, 1RM, and jump performance. Ratings of pain and effort were taken in the first and final training session. An alpha level of p < 0.05 was used to determine significance. There were no between-group differences for any of the morphological or functional variables. The muscle cross sectional area (CSA) increased pre-post training (p = 0.009; CON: 1.6%, BFR-C: 1.1%, BFR-I: 2.2%). Maximal isometric strength increased pre-post training (p < 0.001; CON: 9.6%, BFR-C: 14.3%, BFR-I: 19.3%). Total work performed during an isokinetic endurance task increased pre-post training (p < 0.001, CON: 3.6%, BFR-C: 9.6%, BFR-I: 11.3%). Perceptions of pain (p = 0.026) and effort (p = 0.033) during exercise were higher with BFR-C; however, these reduced with training (p = 0.005-0.034). Overall, these data suggest that when 30% 1RM loads are used with a frequency of 3 times per week, the addition of BFR does not confer superior morphological or functional adaptations in recreationally active individuals. Furthermore, the additional metabolic stress that is proposed to occur with a continuous BFR protocol does not seem to translate into proportionally greater training adaptations. The current findings promote the use of both intermittent BFR and low-load resistance training without BFR, as suitable alternative training methods to continuous BFR. These approaches may be practically applicable for those less tolerable to pain and discomfort associated with ischemia during exercise.
... More specifically, the shape and conduction velocity of the motor unit action potentials are determined by the intrinsic attributes of muscles fibers (6,84) that make up each motor unit, forming the basis for the spectral properties in the EMG. Thus, because ES is mainly composed of type I fibers (9), which seem to be recruited below 40 -50 Hz (17,87), there is a less pronounced response in the 25-to 50-Hz band, and no evolution is observed in the 50-to 150-Hz and 150-to 250-Hz bands. The consistency of the spectral power profiles among subjects from a given group (young/old) and at a given physiological state (rest/exercise) and muscle (leg/back) and the robustness of these profiles at large time scales for repeated rest and exercise segments indicate a universal behavior related to a basic mechanism of muscle tone regulation. ...
... The overall reduced spectral power and the lack of activity at higher frequencies in the old compared with the young group might be explained by the reduction in the discharge rate of motor neurons in old adults (48) and by sarcopenia, the normal decline of skeletal muscle and strength during aging (2,91). Sarcopenia involves primarily type II muscle fibers, which motor units seem to fire above 50 Hz and up to 100 -140 Hz (28,87). ...
... Results for the left back (not shown) are consistent with the results for the right back muscle shown. of different frequency bands to exercise and fatigue of these two muscle types may result from muscle-specific histochemical properties (muscle fiber content) and the distinct role during the squat movement of the VL and ES muscles. According to their fatigue and contractile characteristics, motor units are classified into three major types, slow fatigue᎑resistant, fast fatigue᎑resistant, and fast fatigable motor units, which typically consist of type I, type IIA, and type IIX muscle fibers (7,8,50,63,87). Whereas the back ES muscle is mainly composed of type I slow/oxidative fibers (9,79), the leg VL muscle contains a higher percentage of type II fast/glycolytic fibers (64,83). Furthermore, although both leg and back muscles show high myoelectrical activity during squats, their role during the movement is different; whereas force generation is the primary function of VL, the main role of the ES muscle is trunk stabilization (83). ...
Purpose
The skeletal muscle is an integrated multi-component system with complex dynamics of continuous myoelectrical activation of various muscle types across timescales to facilitate muscle coordination among units and adaptation to physiological states. To understand the multi-scale dynamics of neuromuscular activity, we investigate spectral characteristics of different muscle types across timescales and their evolution with physiological states. We hypothesize that each muscle type is characterized by a specific spectral profile, reflecting muscle composition and function, that remains invariant over timescales and is universal across subjects. Further, we hypothesize that the myoelectrical activation and corresponding spectral profile during certain movements exhibit an evolution path in time that is unique for each muscle type, and reflects responses in muscle dynamics to exercise, fatigue, and aging.
Methods
To probe the multi-scale mechanism of neuromuscular regulation, we develop a novel protocol of repeated squat exercise segments, each performed until exhaustion, and we analyze differentiated spectral power responses over a range of frequency bands for leg and back muscle activation in young and old subjects.
Results
We find that leg and back muscle activation is characterized by muscle-specific spectral profiles, with differentiated frequency bands contribution, and a muscle-specific evolution path in response to fatigue and aging that is universal across subjects in each age group.
Conclusion
The uncovered universality among subjects in the spectral profile of each muscle at a given physiological state, as well as the robustness in the evolution of these profiles over a range of timescales and states, reveals a previously unrecognized multi-scale mechanism underlying the differentiated response of distinct muscle types to exercise-induced fatigue and aging.
Keywords: muscle fibers, spectral power, time scales, fatigue, aging.
... Importantly, the mechanical load normally used in BFR training is considerably lower (i.e. 20-50% of 1 repetition maximum (RM)) compared to heavy resistance training (70-85% of 1-RM) 11 . Further, the same increases in strength may also be achievable by conducting resistance training with low intensity without BFR, however, this would require a substantial increase in the training volume 12 . ...
This study compared perceptional and physiological responses of finger flexor exercise performed with free flow and blood flow restriction (BFR). Thirteen male advanced climbers completed three sessions of finger flexor resistance exercise at (1) 40% of MVC (Low) and (2) 75% of MVC (High) and (3) BFR at 40% of MVC (Low + BFR) in a randomized and counterbalanced order. Rate of perceived exertion for effort (RPE) and discomfort (RPD), session pleasure/displeasure (sPDF), exercise enjoyment (EES), lactate concentration and oxygen saturation were recorded after the last set. Both low-intensity sessions induced higher RPD than High (p = 0.018–0.022, ES = 1.01–1.09) and High was perceived as more enjoyable than Low-BFR (p = 0.031, ES = 1.08). No differences were found for RPE or sPDF (p = 0.132–0.804). Lactate was elevated more after High than the Low-sessions (p < 0.001, ES = 1.88–2.08). Capillary oxygen saturation was lower after Low + BFR compared to the other sessions (p = 0.031, ES = 1.04–1.27). Finally, the exercise volume was greater in Low compared to High (p = 0.022, ES = 1.14) and Low + BFR (p = 0.020, ES = 0.77). In conclusion, among advanced male climbers, performing Low + BFR led to a similar exercise volume but was perceived as more discomforting and less enjoyable compared to High. The Low session yielded similar responses as the Low + BFR but required a much greater exercise volume.
... Recently, it was stated that there is a critical need to report acute physiological responses resulting from exercises performed with different cuff pressures (6). Electromyography (EMG) has often been used in investigations to examine various acute neuromuscular responses such as skeletal muscle excitability (1,(15)(16)(17)(18). For example, as a result of 75 leg extensions distributed across four sets (1×30, 3×15), we reported that the muscle excitation (EMG amplitude [EMG AMP]) recorded during a brief maximum isometric task decreased pretest to post-test following the BFR exercise bout (60% AOP), but not after the non-BFR condition (1). ...
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.
... When a group of motor neurons across several muscles receives a common input from the central nervous system, the corresponding action potentials of the different motor units occur almost simultaneously in multiple muscle areas, leading to an optimal muscle fiber contraction and precise movement (Hug, 2011;Asmussen et al., 2018). Previous studies have demonstrated that slow (type I) and fast (type II) fibers exhibit distinct spectral properties that modulate the spectral distribution of the entire muscle depending on the specific muscle fiber composition (Kupa et al., 1995;Wakeling et al., 2002;Wakeling and Rozitis, 2004;Beck et al., 2007;Wakeling, 2009;Dreibati et al., 2010;Wernbom and Aagaard, 2019;Garcia-Retortillo et al., 2020, Retortillo et al., 2021-with frequencies below 40-60 Hz mainly attributed to the activity of small alpha motor neurons and related type I (oxidative) muscle fibers; 60-120 Hz relate to medium alpha motor neurons and type IIa fibers; and high frequencies 170-220 Hz attributed to the large alpha motor neurons and the innervated by them type IIb (glycolytic) muscle fibers (Grimby et al., 1979(Grimby et al., , 1981Wakeling et al., 2001;Dreibati et al., 2010;Rosenblum et al., 2021). ...
Skeletal muscles continuously coordinate to facilitate a wide range of movements. Muscle fiber composition and timing of activation account for distinct muscle functions and dynamics necessary to fine tune muscle coordination and generate movements. Here we address the fundamental question of how distinct muscle fiber types dynamically synchronize and integrate as a network across muscles with different functions. We uncover that physiological states are characterized by unique inter-muscular network of muscle fiber cross-frequency interactions with hierarchical organization of distinct sub-networks and modules, and a stratification profile of links strength specific for each state. We establish how this network reorganizes with transition from rest to exercise and fatigue—a complex process where network modules follow distinct phase-space trajectories reflecting their functional role in movements and adaptation to fatigue. This opens a new area of research, Network Physiology of Exercise, leading to novel network-based biomarkers of health, fitness and clinical conditions.
... We observed a trend for greater fatigue in the combined NMES and BFR protocol as compared with the other protocols, likely caused by the accumulation of metabolites (attributable to the metabolic stress) resulting from the arterial flow restriction and venous flow blockage (Abe et al., 2006). Both NMES and BFR in combination with voluntary muscle contractions, increases the recruitment of high-threshold motor units (Loenneke et al., 2010;Vanderthommen & Duchateau, 2007), suggesting that fatigue is greater when they are applied simultaneously (Wernbom & Aagaard, 2020). ...
Neuromuscular electrical stimulation (NMES) in combination with blood flow restriction (BFR) enhances muscle hypertrophy and force-generating capacity. The present study aimed to investigate the acute effects of BFR and NMES, both in isolation and in combination, on muscle thickness (MT) and fatigue in the lower body of 20 young healthy subjects. Different stimuli were applied for 25 min, defined by the combination of BFR with high- and low-frequency NMES, and also isolated BFR or NMES. Changes in MT were then evaluated by ultrasound of the rectus femoris (RF) and vastus lateralis (VL) muscles at the end of the session (POST) and 15 min later (POST 15’). Lower limb fatigue was evaluated indirectly by strength performance. Results showed that RF MT was higher under the combined protocol (BFR + NMES) or isolated BFR than under NMES – regardless of the frequency – both at POST (p ≤ 0.018) and POST 15’ (p ≤ 0.016). No significant changes in MT were observed under isolated NMES or BFR at POST 15’ when compared with basal values (p ≥ 0.067). No significant differences were observed for VL MT between conditions (p = 0.322) or for fatigue between conditions (p ≥ 0.258). Our results indicate that a combination of BFR and NMES acutely increases MT in sedentary subjects. Also, although not significantly, BFR conditions had a greater tendency to induce fatigue than isolated NMES.
• Highlights
• The combination of blood flow restriction (BFR) and neuromuscular electrical stimulation (NMES) produces higher acute cell swelling than the isolated application of either NMES or BFR.
• BFR in isolation appears to produce greater cell swelling than NMES, regardless of the frequency used.
• BFR conditions had a greater tendency to induce fatigue than isolated NMES.
... 1 Exercise-induced peripheral fatigue is determined by a multitude of factors including local factors such as pH level, ion distribution, as well as oxygen supply and consumption, for example, through mitochondria. [1][2][3][4][5] Decreased muscle perfusion, for example, due to an NOdeficiency caused by oxidative stress or aging can lead to accelerated fatigue. 3,6 Muscle oxygenation and perfusion are also influenced by systemic factors like hormonal signaling, the ability to reoxygenate blood through an intact lung or the amount of breathing work, all of which are affected by COVID. ...
... Mechanistically, performing exercise in a hypoxic environment increases metabolite accumulation, such as blood lactate and growth hormone (74). This can potentially lead to a greater recruitment of higher threshold motor units and an increased hypertrophy (84). As a result, a load which under normal conditions would require the same amount of work from the muscles or muscle activation now imposes a greater systemic demand and corresponds to a higher percentage of maximal oxygen uptake. ...
A fundamental task in exercise physiology is to determine and ultimately improve the adaptations that take place in the human body, an integrated network of various physiological systems, for example, muscle, tendon, and bone. Investigating the temporal dynamics (time course) of adaptations in these diverse systems may help us gain new knowledge about the functioning of the neuromotor system in healthy and pathological conditions. The aim of this review was to explore the temporal dynamics of muscular strength adaptations in studies implementing a resistance training intervention. In addition, we categorized these studies under mechanical or metabolic stimuli to identify whether certain stimuli cause faster muscle strength gains. Searches were performed using PubMed and Google Scholar databases. The review comprised 708 subjects from 57 training groups within 40 studies that met the inclusion criteria. The results revealed that the mean time point of first significant increase in muscle strength of all studies was 4.3 weeks, and the corresponding increase was on average about 17%. A plateau in muscle strength increase (∼25%) was found to occur between weeks 8 and 12. Categorization into stimuli groups revealed that performing training in a hypoxic environment is likely to produce a leftward shift (∼25% increase at ∼2.8 weeks) in the dose-response relationship compared with blood flow restriction and supplementation. However, stimuli that cause faster muscle strength gains may also induce imbalanced adaptation between the muscle and the surrounding biological structures, potentially triggering a degradation in some parts of the network (i.e., leading to an increased risk of injury).
... There is a vast body of literature demonstrating that performing resistance exercises under BFR acutely reduces force production. [16][17][18] However, the effects of BFR on force production when performing endurance exercises is not yet known. The hypothesis that reductions in torque would be higher following HI (∼29%) than any of the BFR exercise modes was confirmed in this study. ...
Purpose:
The aim of this study was to identify a blood-flow-restriction (BFR) endurance exercise protocol that maximizes metabolic strain and minimizes muscle fatigue.
Methods:
Twelve healthy participants accomplished 5 different interval cycling endurance exercises (2-min work, 1-min rest) in a randomized order: (1) control, low intensity with unrestricted blood flow (CON30); (2) low intensity with intermittent BFR (i-BFR30, ∼150 mm Hg); (3) low intensity with continuous BFR (c-BFR, ∼100 mm Hg); (4) unloaded cycling with i-BFR0 (∼150 mm Hg); and (5) high intensity (HI) with unrestricted blood flow. Force production, creatine kinase activity, antioxidant markers, blood pH, and potassium (K+) were measured in a range of 5 minutes before and after each cycling exercise protocol.
Results:
HI showed the highest reduction (Δ = -0.26 [0.05], d = 5.6) on blood pH. Delta pH for c-BRF30 (Δ = -0.02 [0.03], d = 0.8) and Δ pH for i-BRF30 (Δ = -0.04 [0.03], d = 1.6) were different from each other, and both were higher compared with CON30 (Δ = 0.03 [0.03]). There was significant before-to-after force loss following HI (Δ = 55 [40] N·m-1, d = 1.5) and c-BFR30 (Δ = 27 [21] N·m-1, d = 0.7) protocols only, which were accompanied by significant increases in K+ (HI: Δ = 0.94 [0.65] mmol·L-1, d = 1.8; c-BFR30: Δ = 0.72 [0.85] mmol·L-1, d = 1.2). Moreover, all BFR conditions elicited slight increases in plasma creatine kinase, but not for HI and CON30. Glutathione changes from before to after were significant for all BFR conditions and HI, but not for CON30.
Conclusions:
The attenuation in fatigue-induced reductions in maximal force suggests that i-BFR exercise could be preferable to c-BFR in improving exercise capacity, with considerably less biologic stress elicited from HI exercises.
... Low-load resistance exercise performed with concurrent blood flow restriction (BFR) typically achieved by means of pneumatic cuff compression applied proximally around the exercising limb has repeatedly demonstrated significant improvements in skeletal muscle mass, strength, and functional performance in both healthy, elderly individuals, and clinical populations (10,(14)(15)(16)(17)(18)(19). BFR training is known to create a hypoxic myocellular environment in the working limb, which is suggested to give rise to elevated levels of metabolic stress that may lead to increased type II muscle fibre recruitment (20), myocellular swelling (21), and elevated intramuscular concentrations of metabolites (22) accompanied by increased synthesis of muscle protein. Furthermore, BFR-training has been observed to stimulate the proliferation of myogenic stem cells (satellite cells), which potentially improves the regenerative capacity of the muscle tissue and contributes to the marked muscle hypertrophy observed with this type of training (23). ...
Objective:
To investigate if blood flow restricted walking exercise is feasible in patients suffering from knee osteoarthritis, and secondly to examine changes in functional performance and self-reported function.
Design:
Feasibility study.
Patients and methods:
Fourteen elderly individuals diagnosed with knee osteoarthritis participated in 8-10 weeks of outdoor walking (4 km/h, 20 minutes/session, 4 times/week) with partial blood flow restriction applied to the affected leg. Adherence, drop-outs and adverse events were registered. Timed-Up&Go, 30-s sit-to-stand performance, 40-m fast-paced walk speed, stair-climbing and Knee Osteoarthritis Outcome Score were assessed pre- and post-training.
Results:
Nine participants completed the intervention, while five participants withdrew of which four experienced cuff discomfort or exacerbated knee pain. Baseline BMI (p=0.05) and knee pain (p=0.06) were higher while gait performance (p=0.04) was reduced in non-completing participants. Considering completed case data, training-adherence rate was 93%, while mean knee pain in the affected leg was 0.7 on a numerical rating scale from 0-10. Functional performance improved, while self-reported function remained unchanged.
Conclusion:
Blood flow restricted walking exercise appeared feasible in patients with knee osteoarthritis although possibly affected by participants' baseline characteristics. Participants who completed the intervention protocol demonstrated improvements in functional performance, without any changes in self-reported function.
... Blood flow restricted resistance exercise (BFRRE) can increase muscle size and strength. BFRRE using low loads of 20-50% of 1 repetition maximum (1RM) is suggested for subjects who cannot tolerate high musculoskeletal forces and for trained athletes who reached a plateau in muscle mass and strength [53]. VO 2 max is essential for the assessment of middle-and long-distance running performance. ...
The plateau effect in training is a significant obstacle for professional athletes and average subjects. It evolves from both the muscle-nerve-axis-associated performance and various cardiorespiratory parameters. Compensatory adaptation mechanisms contribute to a lack of continuous improvement with most exercise regimens. Attempts to overcome this plateau in exercise have been only partially successful, and it remains a significant unmet need in both healthy subjects and those suffering from chronic neuromuscular, cardiopulmonary, and metabolic diseases. Variability patterns characterize many biological processes, from cellular to organ levels. The present review discusses the significant obstacles in overcoming the plateau in training and establishes a platform to implement subject-tailored variability patterns to prevent and overcome this plateau in muscle and cardiorespiratory performance.
... Specifically, a powerlifter may have greater growth potential in type I fibers due to a preferential hypertrophy occurred in type II fibers (Bjørnsen et al. 2019). Despite the contrasting results of these studies with respect to preferential muscle hypertrophy, it may be plausible that the interactions between mechanical and ischemic stimuli with BFR may serve as a method to facilitate muscle fatigue (i.e., augmenting muscle activation) in a manner that calf muscles, such as the soleus predominantly consisting of type I fibers, may be exposed to greater stimulation of hypertrophy signaling (Wernbom and Aagaard 2020). Notwithstanding previous studies conducted with untrained (Schoenfeld et al. 2020;Centner et al. 2019) or resistance-trained individuals (without specifying whether or not they have directly trained the calf muscles prior to the participation) (Gavanda et al. 2020), this idea has not been experimentally tested in resistance-trained individuals who regularly perform calf resistance training directly. ...
Purpose
To compare muscle growth adaptations between traditional high-load training and low-load training with blood flow restriction (BFR) in the calf muscles over 6 weeks.
Methods
27 trained individuals performed calf exercise in both legs for 6 weeks. Each leg was randomly assigned to one of the two conditions: (1) Traditional (70% of 1RM) training (TRAD); and (2) Low-load (30% of 1RM) training with BFR. In addition, subjects performed standing calf raises with or without BFR. Measures were taken pre- and post-intervention.
Results
For the posterior muscle site, there was no condition (BFR vs. TRAD) × time (pre vs. post) interaction (p = 0.15). In addition, there was no main effect for condition (p = 0.83) or time (p = 0.20). For the lateral muscle site, there was no condition × time interaction (p = 0.47). In addition, there was no main effect for condition (p = 0.10) or time (p = 0.57). For the medial muscle site, there was no condition × time interaction (p = 0.60). In addition, there was no main effect for condition (p = 0.44) or time (p = 0.72). For RPE, there was no condition × time interaction. However, there was a main effect for condition (p < 0.05) with BFR having higher RPE. For discomfort, there was no condition × time interaction. However, there was a main effect for condition (p < 0.001) with the BFR condition displaying higher discomfort.
Conclusion
No muscle growth was detected in the calf musculature. BFR was not more effective at eliciting muscle hypertrophy compared to traditional training. However, it was accompanied with higher exertion and discomfort.
... The increased functional performance, measured as an improved unilateral sit-to-stand function, may be due to increased lower limb strength. As such exercising with BFR has been suggested to cause tissue hypoxia, an increment in metabolites, and muscle cell swelling, which all contributes to increased protein synthesis, increased type II muscle fiber recruitment, local and systemic anabolic hormone synthesis, and stimulation of myogenic stem cells (Wernbom et al., 2008;Nielsen et al., 2012;Wernbom and Aagaard, 2019;Vopat et al., 2020). Thus, the gains in muscle strength as a result of exercising, would most likely translate into an improved functional performance. ...
Introduction: Reactive arthritis (ReA) is a chronic inflammatory disease usually caused by a preceding gastrointestinal or genitourinary bacterial infection. ReA usually occurs in the lower limbs causing joint pain and joint swelling. Physiotherapy-led exercise is recommended to prevent muscle atrophy. The purpose of this case report is to describe the outcome after 12 weeks of low-load blood flow restricted resistance training (BFR-RT) as a rehabilitation method for a young male suffering from ReA.
Methods and materials: A 17-year-old male suffered from ReA in the both knee joints and the left hip joint. 36 months after the incident, he suffered from another ReA incident in his right knee. Non-steroid anti-inflammatory drugs and a new arthrocentesis added with corticosteroid injection was unsuccessful in treating the ReA. The patient performed 12 weeks of BFR-RT on the right lower limb with a low amount of supervision after the first week of training. Assessment of unilateral 30-sec chair stand test (u30-sec CST), low-thigh circumference above apex patella, The Knee Injury and Osteoarthritis Outcome Score (KOOS), The Forgotten Knee Joint Score (FJS), and Numeric Ranking Scale for pain (NRS) was performed at baseline and after 3,6,9, and 12 weeks of BFR-RT.
Results: The patient completed all planned exercise sessions. u30-sec CST improved with 7 repetitions (reps) on the right limb and 5 reps on the left leg. Low-thigh circumference decreased 1.1 cm on the right leg and 1.0 on the left leg. KOOS symptoms, ADL, quality of life and FJS demonstrated a clinically relevant change on 10, 14 and 23 points.
Conclusion: The present case study indicates that even with low amounts of supervision BFR-RT could increase functional performance, reduce knee joint swelling and improve key patient-reported outcome.
... Originally developed to augment muscle accretion, BFRRE research has predominantly been directed towards improvements in exercise performance and musculoskeletal rehabilitation. The mechanisms underlying the muscle hypertrophic effects of BFRRE have been suggested to be related to heightened growth hormone signaling, mechanical stress adhering to cell swelling from venous pooling on cell pressure or length changes from loaded contractions, as well as altered patterns of neuromuscular recruitment (Pearson and Hussain, 2015;Rindom and Vissing, 2016;Rindom et al., 2019;Wernbom and Aagaard, 2020). Its parallels to RIC are not thoroughly investigated, but many common features exist in the cardioprotective signaling initiated by exercise and RIC. ...
Exposing tissues to brief periods of ischemia confers resistance to subsequent prolonged ischemia (local ischemic preconditioning). Though first described in the tissue undergoing ischemia, a systemic response with protection of remote tissues (remote ischemic conditioning, RIC) can be induced by repeated brief ischemia of a limb. RIC can be applied clinically to reduce infarct size and/or improve outcomes in patients admitted with acute myocardial infarction or stroke. A resembling stimulus and systemic protective effect may be achievable from intermittent occlusion-reperfusion elicited by the contraction-relaxation phases during resistance exercise. Moreover, this stimulus may be further enhanced when practiced with simultaneous blood flow restriction, referred to as blood flow-restricted resistance exercise (BFRRE). While the preconditioning effects of BFRRE and the detailed mechanisms by which RIC and BFRRE may exert protection remain to be defined, RIC has been shown to induce organ protection via systemic mediators acting through direct cytoprotection in the target organ. The protective processes appear to be partly facilitated by extracellular vesicles (EV) carrying micro RNAs (miRNAs) from the site of occlusion to sites of organ damage. Moreover, RIC and exercise regimens may promote tissue rebuilding upon repeated application. However, little is known on the effects of RIC versus BFRRE on acute EV-derived responses and on chronic peripheral skeletal muscle responses. In the current review, with background in the literature and recent experimental discoveries, we discuss the potential of ischemia and/or exercise regimens in promoting peripheral and central organ preconditioning.
... When exercising to fatigue, however, end point metabolic stress tends to be higher after resistance training with lower loads (<35% 1RM) (44)(45)(46)(47)(48)(49) than high loads. The use of lower relative training loads allows for more repetitions to be performed before reaching contraction failure, hence resulting in more sustained metabolic stress (due to more pronounced glycolysis) in a larger part of the active myofibers at the point of contraction failure (50). In the present study BFR20 and FF20 exercise to failure were employed to represent protocols with higher metabolic stress and were therefore predicted to cause larger R 2 decreases than FF20 WM and FF70. ...
Aim:
MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI).
Methods:
The study was a cross-over study with participants (n=10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20WM). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow and diffusion.
Results:
Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20WM and FF70. Only BFR20 caused acute increases in intracellular volume. Post-exercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols.
Conclusion:
This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle.
... This is potentially a result of boys' greater reliance on lower-threshold motor units during exercise. Since BFO training in adults is largely based on the use of higher-threshold (typically type II) motor units (Karabulut et al. 2010;Manimmanakorn et al. 2013;Takarada et al. 2000;Wernbom and Aagaard 2019), it is possible that BFO training may not induce as large an effect for boys. Future low-load BFO resistance training research using larger muscle groups, trials to fatigue, and higher exercise intensities (40-70% MVC) are recommended to determine the effectiveness of such training on long-term muscle adaptations in children as compared to adults. ...
PurposeIn adults, low-load resistance training with blood flow occlusion (BFO) mimics strength increases that occur from high-load training, without the need to experience high mechanical stress. In view of child–adult differences in exercise responses, this study examined whether BFO during exercise elicits differential changes in maximal voluntary contraction (MVC) and electromyographical (EMG) activity in children and adults.Methods
Sixteen men (24.4 ± 2.5 years) and 14 boys (10.7 ± 2.0 years) performed low-load resistance exercise (25 repetitions at 35% MVC) of the wrist flexors with and without BFO. MVC wrist flexor force and EMG activity of the flexor carpi radialis (FCR) were obtained at the beginning and end of the exercise.ResultsBoth groups demonstrated a larger decrease in MVC force following BFO (− 18.6 ± 12.5%) than the control (without BFO) condition (− 6.2 ± 15.0%; p < 0.001). Whereas the men’s EMG amplitude increased 16.3 ± 20.5% (p = 0.005) during BFO, the boys’ EMG amplitude did not change over time or between conditions. In both groups, the mean power frequency (MPF) of the EMG signal decreased more during BFO (− 20.1 ± 9.6%; p < 0.001) than the control condition (− 5.6 ± 9.7%; p = 0.002).Conclusions
Low-load exercise with BFO resulted in similar neuromuscular responses between boys and men, except for an observed increase in the EMG amplitude in men but not boys. While this result might suggest that men relied on a greater activation of higher-threshold motor units during BFO, it does not explain why there were similar decreases in MPF between groups. Therefore, it remains unclear whether the effectiveness of BFO training is similar for children and adults.
... Physical exercise can counteract many cancer promoting factors, such as high inflammatory levels, high levels of adipose tissue, cachexia, cardiovascular diseases [5] and a low mitochondrial capacity. Therefore, researchers are more and more eager to understand the molecular mechanisms that promote the manifold of effects that exercise can have on our physiology [6][7][8][9]. ...
Cancer is a heterogeneous disease which can influence many facets of the human physiology. Treatments and therapies of cancer are as diverse as the illness itself and often come with toxic side effects. In many reviews, researchers regularly summarize the newest results and try to untangle the complexity of cancer and cancer‐related research [1]. This review aims to connect recent research on the field of molecular biology of cancer with recent results from exercise physiology that were published in Acta Physiologica.
... When monitoring myocellular swelling, R 2 measures can be combined with measures of cross-sectional area (CSA) obtained from the raw MRI images and diffusion. Diffusion by itself, on the other hand, is less specific, as it is affected by several biological factors that have been associated with exercise, including microfiber damage, membrane permeability, metabolite concentrations, and levels of inflammation (49,66). ...
Aim:
Important physiological quantities for investigating muscle hypertrophy include blood oxygenation, cell swelling and changes in blood flow. The purpose of this study was to compare the acute changes of these parameters in human skeletal muscle induced by low-load (20% 1RM) blood flow restricted (BFR-20) knee extensor exercise compared to free-flow work matched (FF-20WM) and free flow 50% 1 RM (FF-50) knee extensor exercise using multi-modal magnetic resonance imaging (MRI).
Methods:
Subjects (n=11) completed acute exercise sessions for each exercise mode in an MRI scanner where interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), blood flow and diffusion were performed before, during and after each exercise protocol.
Results:
BFR-20 exercise resulted in larger acute decreases in R2 and greater increases in cross-sectional area than FF-20WM and FF-50 (p<0.01). Blood oxygenation decreased between sets during BFR-20 as indicated by a 13.6% increase in R2' values (p<0.01)), while unchanged for FF-20WM and decreased during FF-50 exercise. Quadriceps blood flow between sets was highest for the heavier load (FF-50) averaging 305 ml/min and lowest for BFR-20 at 123 ± 73 ml/min until post-exercise cuff release, where blood flow rates in BFR-20 exceeded both FF protocols (p<0.01). Acute changes in diffusion rates were similar for all exercise protocols.
Conclusion:
This study was able to differentiate the acute exercise response of selected physiological factors associated with skeletal muscle hypertrophy. Marked differences in these parameters were found to exist between BFR and FF exercise conditions.
... In this context it needs to be highlighted, however, that all the studies presented here and in the present review used bipolar surface EMG to measure muscle excitation. This can be problematic as changes in EMG cannot unambiguously be attributed to changes in motor unit (MU) recruitment and firing because additional influences such as muscle fiber potential, motor unit synchronization and fatigue can influence the EMG amplitude (Wernbom and Aagaard, 2020). With the course of technological advancements, Fatela et al. (2019) non-invasively estimated MU recruitment and firing rates by means of highdensity EMG and decomposition techniques. ...
Objective: To summarize the existing evidence on the long-term effects of low-load (LL) blood flow restricted (BFR) exercise on neural markers including both central and peripheral adaptations.
Methods: A systematic review and meta-analysis was conducted according to the PRISMA guidelines. The literature search was performed independently by two reviewers in the following electronic databases: PubMed, Web of Science, Scopus and CENTRAL. The systematic review included long-term trials investigating the effects of LL-BFR training in healthy subjects and compared theses effects to either LL or high-load (HL) training without blood flow restriction.
Results: From a total of N = 4499 studies, N = 10 studies were included in the qualitative synthesis and N = 4 studies in a meta-analysis. The findings indicated that LL-BFR resulted in enhanced levels of muscle excitation compared to LL training with pooled effect sizes of 0.87 (95% CI: 0.38–1.36). Compared to HL training, muscle excitation following LL-BFR was reported as either similar or slightly lower. Differences between central activation between LL-BFR and LL or HL are less clear.
Conclusion: The summarized effects in this systematic review and meta-analysis highlight that BFR training facilitates neural adaptations following LL training, although differences to conventional HL training are less evident. Future research is urgently needed to identify neural alterations following long-term blood flow restricted exercise.
... Low-load blood flow restricted resistance exercise (low-load BFRRE, henceforth BFRRE) has been suggested as a strategy to reduce mechanical loading and work volume while still evoking gains in muscle mass comparable or sometimes exceeding that of conventional HLRE (6). The principles of BFRRE and some potential underlying mechanisms have been addressed in previous reviews (7)(8)(9). With regard to BFRRE principles, these can be briefly summarized to comprise (I) utilization of equipment (typically inflatable cuffs) and standardization to achieve partial occlusion of arterial blood flow and near-complete/complete occlusion of venous blood flow; (II) low loading, typically in the range of 20%-50% of maximum dynamic strength; (III) exercise repetitions typically performed to a state of near or complete volitional failure; and (IV) very short interset recovery with occlusion maintained. ...
Low-load blood flow restricted resistance exercise (BFRRE) can stimulate whole-muscle growth and improve muscle function. However, limited knowledge exists on the effects at the myocellular level. We hypothesize that BFRRE possesses the ability to produce concurrent skeletal muscle myofibrillar, mitochondrial, and microvascular adaptations, thus offering an alternative strategy to counteract decay in skeletal muscle health and function in clinical populations.
... Byproducts of muscular contractions such as lactate, hydrogen ions (H+), ATP, and inorganic phosphates are produced and are unable to exit the limb through the venous system due to the restrictive cuff (56). These metabolites interfere with the excitation-contraction mechanism causing earlier recruitment of type 2 muscle fibers relative to the same exercise being performed in free-flow conditions (22,98). As fatigue accumulates from the metabolic stress, muscle contraction velocity slows and muscle activation increases (85), ultimately stimulating anabolic processes. ...
Emerging evidence indicates that low load blood flow restriction (BFR) training is an effective strategy to increase muscular adaptations. Yet, it remains questionable as to whether combining BFR with traditional resistance training can potentiate hypertrophic adaptations. The purpose of this article is to provide an evidence-based review of current research on the topic including underlying mechanisms of BFR training and draw practical conclusions as to how BFR can be applied by physique athletes to optimize increases in muscle mass.
... BFR resistance training involves the application of a cuff around the most proximal portion of an exercising limb (arm or leg), inflating the cuff to a pressure predetermined to restrict venous return while keeping arterial flow unimpeded, and completing a low load, high repetition, low rest training protocol under this mild restriction of vascular flow (Pope et al. 2013;Wilk et al. 2018). As publications using this model have emerged, greater research interest in BFR resistance training has focused on BFR exercise as tool for enhancing skeletal muscle hypertrophy and strength in athletes, older-age, or clinical populations (Abe et al. 2006;Scott et al. 2016;Kambič et al. 2019;Wernbom and Aagaard 2019). ...
PurposeResistance exercise induces muscle growth and is an important treatment for age-related losses in muscle mass and strength. Myokines are hypothesized as a signal conveying physiological information to skeletal muscle, possibly to “fine-tune” other regulatory pathways. While myokines are released from skeletal muscle following contraction, their role in increasing muscle mass and strength in response to resistance exercise or training is not established. Recent research identified both local and systemic release of myokines after an acute bout of resistance exercise. However, it is not known whether myokines with putative anabolic function are mechanistically involved in producing muscle hypertrophy after resistance exercise. Further, nitric oxide (NO), an important mediator of muscle stem cell activation, upregulates the expression of certain myokine genes in skeletal muscle.Method
In the systemic context of complex hypertrophic signaling, this review: (1) summarizes literature on several well-recognized, representative myokines with anabolic potential; (2) explores the potential mechanistic role of myokines in skeletal muscle hypertrophy; and (3) identifies future research required to advance our understanding of myokine anabolism specifically in skeletal muscle.ResultThis review establishes a link between myokines and NO production, and emphasizes the importance of considering systemic release of potential anabolic myokines during resistance exercise as complementary to other signals that promote hypertrophy.Conclusion
Investigating adaptations to resistance exercise in aging opens a novel avenue of interdisciplinary research into myokines and NO metabolites during resistance exercise, with the longer-term goal to improve muscle health in daily living, aging, and rehabilitation.
... This could help explain why low-load BFR-RE to concentric contraction failure did not result in greater increases in muscle strength and size than BFR-RE with submaximal exertion after 8 weeks of thrice-weekly training (Sieljacks et al., 2019). In addition, high-volumes of low-load BFR-RE could result in more of a local endurance training stimulus, which may attenuate the hypertrophic responses (discussed in Aagaard, 2020 andSieljacks et al., 2019). ...
... In light of this, it is interesting that similar non length-specific strength gains were observed for both training lengths. This indicates that activation of the muscle with intended maximal effort during training is an important element in the stimulus for strength gains, regardless of the work/torque produced in the contractions, a finding which in some aspects is analogous to findings with blood flow restricted training, where significant strength gains can be achieved despite the load lifted is considerably lower than in conventional strength training (Wernbom and Aagaard, 2019). ...
The purpose of this study was to compare the effect of a 6-week period of knee flexion strength training at either optimal or short muscle length, on length-specific muscle strength and fatigue. Twelve healthy volunteers performed dynamic (isokinetic concentric) training with one leg at short and the contralateral leg at optimal muscle length for 6 weeks. Knee flexor muscle strength was assessed before and after training, comprising maximal voluntary isometric and dynamic contractions at short, intermediate and near optimal muscle length and electrically evoked, contractions at near optimal length only. Fatigability was tested by performing 60 maximal concentric contractions at either short or optimal muscle length. Isometric torque at all muscle lengths improved equally by training at short and optimal muscle length, for example, tested at short 18 (17) versus 21 (17) % (CI) and at optimal 14 (8) versus 17 (16) % muscle length, respectively. Likewise, equal improvements were observed for dynamic contractions in both groups. Prior to training, fatigue induced at optimal muscle length tended to be more pronounced than at short muscle length (fatigue-indexes -41 (6) vs. -34 (7) %, respectively, P = 0.05). However, training at either length did not reduce fatigability. Training with maximal concentric contractions at either short or optimal muscle length for 6 weeks improved isometric and dynamic muscle strength in the entire range of motion without inducing any discernible length-specific adaptations. However, strength training at restricted muscle length did not reduce relative fatigue when induced at either short or optimal muscle length.
Objective
To systematically evaluate the impact of acupuncture on exercise-induced fatigue (EIF).Methods
Scopus, Springer Link, Web of Science, PubMed, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Academic Journal Full-text Database (Wanfang), Chongqing VIP Database (CQVIP), and China Biology Medicine Disc (CBM) were systematically searched to identify randomized controlled trials (RCTs) studying acupuncture treatment of EIF from the inception till August 2020. The risk of bias in the included studies was assessed using the Cochrane handbook. RevMan 5.3 was used to conduct statistical analysis on the extracted data.ResultsA total of 11 RCTs were included for meta-analysis, involving 531 patients. It was revealed that acupuncture produced more significant effects in alleviating subjective fatigue [standardized mean difference (SMD)=−3.08, 95% confidence interval (CI) (−4.35, −1.81), P<0.001], increasing the hemoglobin content [weighted mean difference (WMD)=3.89, 95%CI (1.37, 6.42), P=0.003], reducing the lactate dehydrogenase content [WMD=−10.63, 95%CI (−17.67, −3.59), P=0.003], reducing the blood lactic acid content [SMD=−2.65, 95%CI (−4.47, −0.83), P=0.004], and down-regulating the levels of serum creatine kinase [SMD=−0.79, 95%CI (−1.10, −0.48), P<0.001] and blood urea nitrogen [WMD=−1.47, 95%CI (−1.84, −1.11), P<0.001] than the control groups.Conclusion
Based on the existing evidence, acupuncture can be recognized as effective in improving EIF and is worthy of promotion in clinical settings.
Abstract Strength training (ST) with blood flow restriction (BFR) is known to promote increases in hypertrophy and strength sometimes similar to traditional ST despite the effects of the arterial BFR on muscle adaptations and safety are not well established. The aim of this study was to assess whether ST with arterial BFR is able to improve muscular adaptations, performance and its safety in Wistar rats. Animals aging 8 weeks were divided in four groups: sedentary sham (S/S), sedentary with arterial BFR (S/BFR), trained sham (T/S), and trained with arterial BFR (T/BFR). Training protocol consisted of four weeks of ST composed by six sets of 10 ladder climbing with 50% of 1 maximal voluntary contraction. Body weight, epididymal fat, maximum loaded weight, manual grip strength, muscular hypertrophy index, systolic blood pressure, enzyme activity of superoxide dismutase, nitrite/nitrate concentration and tumor necrosis factor alpha were analyzed. The BFR rate was between 36% and 38%. T/BRF was effective to promote strength and hypertrophy. T/S is an alternative to improve strength, but it did not promote hypertrophy. Furthermore, we found no significant cardiac and metabolic changes. Thus, T/BFR is able to improve muscle adaptations and performance in rats, without causing cardiovascular and metabolic damage.
Studies have shown that strength training (ST) with blood flow restriction (BFR) in which low load is used (20–50% of 1 maximum voluntary contraction - MVC) can produce positive adaptations similar to ST with loads equal to or greater than 70% 1 MVC. Furthermore, recent studies have investigated the effects of STBFR on muscle adaptations, but few studies investigated the effects of STBFR on vascular function. This study aimed to evaluate the effects of the STBFR program on the vascular reactivity of the abdominal aorta of Wistar rats with femoral arteriovenous blood flow restriction. Male rats were divided into four groups: sedentary sham (S/S), sedentary with blood flow restriction (S/BFR), trained sham (T/S), and trained with blood flow restriction (T/BFR). The animals in the S/BFR and T/BFR groups underwent surgery to BFR in the femoral artery and vein. After one week, the trained groups started the ST which consisted of climbing ladder, six sets of 10 repetitions with 50% of 1 MVC assessed by maximum loaded weight (MLW) carried out for four weeks. Concentration-response curves to Acetylcholine (ACh: 10 nM - 100 μM) and Phenylephrine (PHE: 1 nM - 30 μM) were performed in aortic rings with intact endothelium. The production of nitric oxide (NO) and reactive oxygen species (ROS) in situ and the vascular remodeling marker (MMP-2) were also measured. The ST increased the strength of the T/S and T/BFR groups in MLW tests. The S/BFR group showed a 22% reduction in relaxation to acetylcholine, but exercise prevented this reduction in the T/BFR group. In animals without BFR, ST did not alter the response to acetylcholine. An increase in NO production was seen in T/S and T/BFR showed a reduction in ROS production (62% and 40%, respectively). In conclusion low load ST with BFR promotes similar vascular function responses to ST without BFR. Low load ST with and without BFR is interventions that can improve performance with similar magnitudes. Both training methods could have some benefits for vascular health due to NO production in the aorta increased in the T/S group and decreased production of reactive oxygen species in the T/BFR group.
Introdução: Desordens musculoesqueléticas são comuns e podem comprometer a função, o desempenho físico e a qualidade de vida. Dentre as intervenções utilizadas no manejo de desordens musculoesqueléticas, as modalidades de restrição de fluxo sanguíneo (RFS) vêm ganhando espaço na literatura científica. Objetivos: Essa tese teve o propósito de investigar os aspectos fisiológicos, os métodos de prescrição e as aplicações clínicas de modalidades de RFS em diferentes desordens musculoesqueléticas. Métodos e resultados: As modalidades de RFS consideradas foram a RFS passiva (sem exercício concomitante), o pré-condicionamento isquêmico (PCI) e a RFS combinada ao exercício. Como desordens musculoesqueléticas foram consideradas condições que causassem prejuízo funcional, tais como perda de força e de massa muscular, dano muscular induzido por exercício, fadiga muscular e osteoartrite (OA) de joelho. A presente tese é composta por introdução, três capítulos referentes às modalidades de RFS, e considerações finais. Os capítulos 1, 2 e 3 versam, respectivamente, sobre RFS passiva, PCI e RFS combinada ao exercício, e são compostos de sete artigos científicos envolvendo três desenhos de estudo: revisão sistemática (com e sem meta-análise), revisão narrativa e ensaio clínico aleatorizado. O capítulo 1 é uma revisão sistemática (artigo 1) sobre os efeitos da RFS passiva para minimizar perdas de força e de massa muscular (hipotrofia por desuso) em indivíduos submetidos a restrições na descarga de peso em membros inferiores. No capítulo 1 observamos que embora potencialmente útil, o alto risco de viés apresentado nos estudos originais limita a indicação de RFS passiva como modalidade eficaz contra a redução de força e de massa muscular induzida por imobilismo. O capítulo 2 é um ensaio clínico controlado e aleatorizado (artigo 2) que investigou os efeitos do PCI na proteção contra o dano muscular induzido por exercício (DMIE) em pessoas saudáveis. O artigo 2 apontou que o PCI não foi superior ao sham para proteger contra o DMIE. O capítulo 3 aborda aspectos fisiológicos, metodológicos e clínicos da RFS combinada ao exercício físico. O primeiro manuscrito do capítulo 3 (artigo 3) é uma revisão sistemática com meta-análise que analisou a excitação muscular (por eletromiografia de superfície) durante exercício resistido com RFS. O artigo 3 indicou que a excitação muscular durante o exercício de baixa carga com RFS foi maior que durante exercício de carga pareada sem RFS somente quando a falha muscular não foi alcançada. Adicionalmente, exercício de baixa carga com RFS apresentou menor excitação muscular que exercício de alta carga, independentemente de alcançar ou não a falha voluntária. O segundo manuscrito do capítulo 3 (artigo 4) é uma revisão sistemática com meta-análise que mostrou uma
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antecipação da falha muscular durante exercícios de baixa carga com altas pressões de RFS, mas não com baixas pressões. O terceiro manuscrito do capítulo 3 (artigo 5) é uma revisão narrativa que discute a possível necessidade de ajustar a pressão de RFS ao longo das semanas de treinamento. No artigo 5 observamos que a literatura é contraditória, o que dificulta recomendar se tais ajustes na pressão de RFS são necessários. O artigo 6 é um protocolo de ensaio clínico aleatorizado proposto para investigar os efeitos do exercício de baixa carga e volume total reduzido com RFS versus treinamento de alta carga sem RFS no tratamento da OA de joelho. O artigo 7 é o ensaio clínico aleatorizado que apresenta os resultados do protocolo (artigo 6) e mostrou que o treinamento de baixa carga com volume total reduzido e com RFS teve efeito similar ao treinamento de alta carga sem RFS na dor no joelho, desempenho muscular, função física e qualidade de vida de pacientes com OA de joelho, embora a magnitude nos ganhos de força tenha sido maior após treino de alta carga. Conclusões: De forma geral, com exceção do PCI para proteger contra o DMIE, as modalidades de RFS são potencialmente úteis no manejo das disfunções musculoesqueléticas aqui estudadas. Adicionalmente, concluímos que é necessário avançar no entendimento dos mecanismos fisiológicos e no estudo dos métodos de prescrição das diferentes modalidades de restrição de fluxo sanguíneo.
Blood flow restriction (BFR) with low-load resistance exercise (RE) is often used as a surrogate to traditional high-load RE to stimulate muscular adaptations, such as hypertrophy and strength. However, it is not clear whether such adaptations are achieved through similar cellular and molecular processes. We compared changes in muscle function, morphology and signaling pathways between these differing training protocols. Twenty-one males and females (mean ± SD: 24.3 ± 3.1 years) experienced with resistance training (4.9 ± 2.6 years) performed nine weeks of resistance training (three times per week) with either high-loads (75-80% 1RM; HL-RT), or low-loads with BFR (30-40% 1RM; LL-BFR). Before and after the training intervention, resting muscle biopsies were collected, and quadricep cross-sectional area (CSA), muscular strength and power were measured. Approximately 5 days following the intervention, the same individuals performed an additional 'acute' exercise session under the same conditions, and serial muscle biopsies were collected to assess hypertrophic- and ribosomal-based signaling stimuli. Quadricep CSA increased with both LL-BFR (7.4±4.3%) and HL-RT (4.6±2.9%), with no significant differences between training groups (p=0.37). Muscular strength also increased in both training groups, but with superior gains in squat 1RM occurring with HL-RT (p<0.01). Acute phosphorylation of several key proteins involved in hypertrophy signaling pathways, and expression of ribosomal RNA transcription factors occurred to a similar degree with LL-BFR and HL-RT (all p>0.05 for between-group comparisons). Together, these findings validate low-load resistance training with continuous BFR as an effective alternative to traditional high-load resistance training for increasing muscle hypertrophy in trained individuals.
Objectives: To compare the short- and long-term effects of low load blood flow restriction (LL-BFR) versus low- (LL-RT) or high-load (HL-RT) resistance training with free blood flow on myoelectric activity, and investigate the differences between failure and non-failure protocols.
Data Source: We identified sources by searching the MEDLINE/PUBMED, CINAHL, WEB OF SCIENCE, CENTRAL, SCOPUS, SPORTDiscus, and PEDro electronic databases.
Study Selection: We screened titles and abstracts of 1048 articles using our inclusion criteria. A total of 39 articles were selected for further analysis.
Data Extraction: Two reviewers independently assessed the methodological quality of each study and extracted data from studies. A meta-analytic approach was used to compute standardized mean differences (SMD ± 95% confidence intervals (CI)). Subgroup analyses were conducted for both failure or non-failure protocols.
Data Synthesis: The search identified n = 39 articles that met the inclusion criteria. Regarding the short-term effects, LL-BFR increased muscle excitability compared with LL-RT during non-failure exercises (SMD 0.61, 95% CI 0.34 to 0.88), whereas HL-RT increased muscle excitability compared with LL-BFR regardless of voluntary failure (SMD −0.61, 95% CI −1.01 to 0.21) or not (SMD −1.13, CI −1.94 to −0.33). Concerning the long-term effects, LL-BFR increased muscle excitability compared with LL-RT during exercises performed to failure (SMD 1.09, CI 0.39 to 1.79).
Conclusions: Greater short-term muscle excitability levels are observed in LL-BFR than LL-RT during non-failure protocols. Conversely, greater muscle excitability is present during HL-RT compared with LL-BFR, regardless of volitional failure. Furthermore, LL-BFR performed to failure increases muscle excitability in the long-term compared with LL-RT.
Background
There is a lack of evidence of the relative effects of different exercise modes on pain sensitization and pain intensity in individuals with knee osteoarthritis (KOA).
Methods
Ninety individuals with radiographic and symptomatic KOA, ineligible for knee replacement surgery, were randomized to 12 weeks of twice‐weekly strength training in addition to neuromuscular exercise and education (ST+NEMEX‐EDU) or neuromuscular exercise and education alone (NEMEX‐EDU). Outcomes were bilateral, lower‐leg, cuff pressure pain‐ and tolerance thresholds (PPT, PTT), temporal summation (TS), conditioned pain modulation (CPM), self‐reported knee pain intensity, and number of painful body sites.
Results
After 12 weeks of exercise, we found significant differences in increases in PPT (‐5.01 kPa (‐8.29 to ‐1.73, p=0.0028)) and PTT (‐8.02 kPa (‐12.22 to ‐3.82, p=0.0002)) in the KOA leg in favor of ST+NEMEX‐EDU. We found no difference in effects between groups on TS, CPM or number of painful body sites. In contrast, there were significantly greater pain‐relieving effects on VAS mean knee pain during the last week (‐8.4 mm (‐16.2 to ‐0.5, p=0.0364) and during function (‐16.0 mm (‐24.8 to ‐7.3, p=0.0004)) in favor of NEMEX‐EDU after 12 weeks of exercise.
Conclusion
Additional strength training reduced pain sensitization compared to neuromuscular exercise and education alone, but also attenuated the reduction in pain intensity compared to neuromuscular exercise and education alone. The study provides the first dose‐ and type‐specific insight into the effects of a sustained exercise period on pain sensitization in KOA. Future studies are needed to elucidate the role of different exercise modes.
Last year, in many ways, was remarkable, also for Acta Physiologica. Strangely, manuscript submissions did not surge during the most rigid periods of lockdown in March and April. Too stunned by the events, not many scientists swapped their pipette for the fountain pen to bring to paper what had long been on their minds. We actually observed an 8%‐decline in submissions during these two months. However, in the end, submissions to Acta Physiologica was up by 7%, thus continuing the constant rise of manuscript sent to us for consideration.¹ In only two years, submissions increased by more than 50%.
Introduction: Up to 20% of patients undergoing total knee replacement (TKR) surgery report no or suboptimal pain relief after TKR. Moreover, despite chances of recovering to preoperative functional levels, patients receiving TKR have demonstrated persistent deficits in quadriceps strength and functional performance compared with healthy age-matched adults. We intend to examine if low-load blood flow restricted exercise (BFRE) is an effective preoperative method to increase functional capacity, lower limb muscle strength and self-reported outcomes after TKR. In addition, the study aims to investigate to which extent preoperative BFRE will protect against surgery-related atrophy 3 months after TKR.
Methods: In this multicentre, randomised controlled and assessor blinded trial, 84 patients scheduled for TKR will be randomised to receive usual care and 8 weeks of preoperative BFRE or to follow usual care-only. Data will be collected before randomisation, 3-4 days prior to TKR, 6 weeks, 3 months and 12 months after TKR. Primary outcome will be the change in 30 s chair stand test from baseline to 3-month follow-up. Key secondary outcomes will be timed up and go, 40 me fast-paced walk test, isometric knee extensor and flexor strength, patient-reported outcome and selected myofiber properties.Intention-to-treat principle and per-protocol analyses will be conducted. A one-way analysis of variance model will be used to analyse between group mean changes. Preintervention-to-postintervention comparisons will be analysed using a mixed linear model. Also, paired Student's t-test will be performed to gain insight into the potential pretraining-to-post-training differences within the respective training or control groups and regression analysis will be used for analysation of associations between selected outcomes.
Ethical approval: The trial has been accepted by the Central Denmark Region Committee on Biomedical Research Ethics (Journal No 10-72-19-19) and the Danish Data Protection Agency (Journal No 652164). All results will be published in international peer-reviewed scientific journals regardless of positive, negative or inconclusive results.
Purpose of Review
Blood flow restriction (BFR) exercise is a recent and novel intervention showing promising results in counteracting several physiological effects related to aging, leading to disability in older adults. The purpose of this paper is to review recent literature within the last 5 years on the effectiveness of BFR training in older adults.
Recent Findings
BFR performed during light load (20–30% of one-repetition maximum) resistance exercise have showed to enhance musculoskeletal and cardiometabolic health in healthy and frail older adults without any adverse events. Other novel findings are improvements in mobility and gait after performing a BFR training intervention.
Summary
Including BFR simultaneously with resistance exercise increases bone and muscle mass primarily through several hormonal pathways at the same time it enhances cardiovascular function without any adverse events. The improvements in mobility and gait are indicators of greater health-related quality of life minimizing disability in older adults.
Objective
We tested the safety, feasibility and effectiveness of blood flow restriction‐empowered low‐intensity interval walking exercise (BFR‐W) compared with conventional intensive overground walking (CON‐W) at improving gait speed and functional capacity in patients with multiple sclerosis (MS) and severe gait disabilities.
Methods
24 patients (58±5 years; 7 males) with progressive MS (Expanded Disability Status Scale 5.5−6.5) were randomized to receive 12 rehabilitation sessions over 6 weeks. The BFR‐W group (n=12) performed interval walking (speed paced by a metronome that increased weekly) with BFR bands at the thighs. The CON‐W group (n=12) received physiotherapist‐assisted overground walking therapy. The primary outcome was gait speed, measured by the timed 25‐foot walk test. Secondary outcomes included walking endurance, balance, strength, fatigue and quality of life. The measurements were collected at baseline, at the end of training and a 6‐week follow‐up.
Results
The two groups did not present any baseline difference. BFR‐W group safely walked without limitations due to sleeve compression, with lower increase of perceived exertion (RPE) (p<0.001) and heart rate (p=0.031) compared with the CON‐W. Gait speed improved significantly in both groups (BFR‐W +13%; CON‐W +5%) with greater increases in the BFR‐W group at end of the training (p=0.001) and at the follow‐up (p=0.041). Most of the secondary outcomes significantly improved in the two groups, without between‐group differences.
Conclusions
Slow interval walking with moderate BFR to the lower limbs was superior to overground walking in improving gait speed in patients with MS with a lower training load and a more durable clinical benefit.
Introduction:
Heavy-load strength training (HLT) is generally considered the Gold Standard exercise modality for inducing gains in skeletal muscle strength. However, use of heavy external exercise loads may be contraindicative in frail individuals. Low-load resistance exercise combined with partial blood-flow restriction (LL-BFR exercise) may offer an effective alternative for increasing mechanical muscle strength and size. The aim of this study was to compare the effect of LL-BFR training to HLT on maximal muscle strength gains. Prospero registration-id (CRD42014013382).
Materials and methods:
A systematic search in six healthcare science databases and reference lists was conducted. Data selected for primary analysis consisted of post intervention changes in maximal muscle strength. A random effects meta-analysis with standardized mean differences (SMD) was used.
Results:
Of 1413 papers identified through systematic search routines, sixteen papers fulfilled the inclusion criteria, totalling 153 participants completing HLT and 157 completing LL-BFR training. The magnitude of training-induced gains in maximal muscle strength did not differ between LL-BFR training and HLT (SMD of -0.17(95% CI: -0.40; 0.05)). Low between-study heterogeneity was noted (I2 =0.0%, Chi2 p=9.65).
Conclusion:
LL-BFR training appears equally effective of producing gains in maximal voluntary muscle strength compared to HLT in 20-to-80-year-old healthy and habitually active adults.
Abstract
PURPOSE: To investigate muscle hypertrophy, strength, myonuclear and satellite cell (SC) responses to high-frequency blood flow restricted resistance exercise (BFRRE). METHODS: Thirteen individuals (24±2 years [mean ± SD], 9 males) completed two 5-day-blocks of 7 BFRRE sessions, separated by a 10-day rest period. Four sets of unilateral knee extensions to voluntary failure at 20% of 1RM were conducted with partial blood flow restriction (90-100 mmHg). Muscle samples obtained before-, during, 3- and 10 days after training were analyzed for muscle fiber area (MFA), myonuclei, SC, and mRNA and miRNA expression. Muscle size was measured by ultrasonography and magnetic resonance imaging, and strength with 1RM knee-extension. RESULTS: With the first block of BFRRE, SC number increased in both fiber types (70-80%, p<0.05), while type I and II MFA decreased by 6±7% and 15±11% (p<0.05), respectively. With the second block of training, muscle size increased by 6-8%, while the number of SC (type I: 80±63%, type II 147±95%), myonuclei (type I: 30±24%, type II: 31±28%) and MFA (type I: 19±19%, type II: 11±19%) peaked 10 days after the second block of BFRRE, whereas strength peaked after 20 days of detraining (6±6%, p<0.05). Pax7- and p21 mRNA expression were elevated during the intervention, while myostatin, IGF1R, MyoD, myogenin, cyclinD1 and -D2 mRNA did not change until 3-10 days post intervention. CONCLUSION: High frequency low-load BFRRE induced robust increases in SC, myonuclei and muscle size, but modest strength gains. Intriguingly, the responses were delayed and peaked 10-20 days after the training intervention, indicating overreaching.
Low‐load blood flow restricted resistance exercise (BFRE) performed to volitional failure is suggested to constitute an effective method for producing increases in muscle size and function. However, failure BFRE may entail high levels of perceived exertion, discomfort and/or delayed onset of muscle soreness (DOMS). The aim of the study was to compare BFRE performed to volitional failure (F‐BFRE) vs non‐failure BFRE (NF‐BFRE) on changes in muscle size, function and perceptual responses. Fourteen young untrained males had one leg randomized to knee‐extension F‐BFRE while the contralateral leg performed NF‐BFRE. The training consisted of 22 training bouts over an 8‐week period. Whole‐muscle cross‐sectional area (CSA) of quadriceps components, muscle function, and DOMS were assessed before and after the training period. Perceived exertion and discomfort were registered during each training bout. Both F‐BFRE and NF‐BFRE produced regional increases in muscle CSA in the range of; quadriceps (2.5‐3.8%), vastus lateralis (8.1‐8.5%), and rectus femoris (7.9‐25.0%). All without differences between leg. Muscle strength (6.8‐11.5%) and strength‐endurance capacity (13.9‐18.6%) also increased to a similar degree in both legs. Less perceived exertion, discomfort and DOMS were reported with NF‐BFRE compared to F‐BFRE. In conclusion, non‐failure BFRE enable increases in muscle size and muscle function, while involving reduced perceptions of exertion, discomfort and DOMS. Non‐failure BFRE may be a more feasible approach in clinical settings.
This article is protected by copyright. All rights reserved.
Purpose:
To investigate the effects of blood flow restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. METHODS
Seventeen national level powerlifters (25±6 yrs [mean±SD], 15 men) were randomly assigned to either a BFRRE group (n=9) performing two blocks (week 1 and 3) of five BFRRE front squat sessions within a 6.5-week training period, or a conventional training group (Con; n=8) performing front squats at ~70% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross sectional areas (CSA) of VL and m. rectus femoris (RF) were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat.
Results:
BFRRE induced selective type I fiber increases in MFA (BFRRE: 12% vs. Con: 0%, p<0.01) and myonuclear number (BFRRE: 17% vs. Con: 0%, p=0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs. 0.5%, p=0.04), which correlated with the increases in MFA of type I fibers (r=0.81, p=0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (p=0.04), whereas 1RM increased in Con (p=0.02).Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibres of national level powerlifters.
Once assumed only to be a waste product of anaerobe glycolytic activity, lactate is now recognized as an energy source in skeletal muscles. While lactate metabolism has been extensively studied in vivo, underlying cellular processes are poorly described. This study aimed to examine lactate metabolism in cultured human myotubes and to investigate effects of lactate exposure on metabolism of oleic acid and glucose. Lactic acid, fatty acid and glucose metabolism were studied in myotubes using [14C(U)]lactic acid, [14C]oleic acid and [14C(U)]glucose, respectively. Myotubes expressed both the MCT1, MCT2, MCT3 and MCT4 lactate transporters, and lactic acid was found to be a substrate for both glycogen synthesis and lipid storage. Pyruvate and palmitic acid inhibited lactic acid oxidation, whilst glucose and α-cyano-4-hydroxycinnamic acid inhibited lactic acid uptake. Acute addition of lactic acid inhibited glucose and oleic acid oxidation, whereas oleic acid uptake was increased. Pretreatment with lactic acid for 24 h did not affect glucose or oleic acid metabolism. By replacing glucose with lactic acid during the whole culturing period, glucose uptake and oxidation were increased by 2.8-fold and 3-fold, respectively, and oleic acid oxidation was increased 1.4-fold. Thus, lactic acid has an important role in energy metabolism of human myotubes.
Low force exercise training with blood flow restriction (BFR) elicits muscle hypertrophy. We investigated the effects of microvascular hypoxia (i.e., low microvascular O2partial pressures, PmvO2) during contractions on hypertrophic signaling, growth response and key muscle adaptations for increasing exercise capacity. Wistar rats were fitted with a cuff placed around the upper thigh and inflated to restrict limb blood flow. Low force isometric contractions (30 Hz) were evoked via electrical stimulation of the tibialis anterior (TA) nerve. The PmvO2was determined by phosphorescence quenching. Rats underwent acute and chronic stimulation protocols. PmvO2decreased transiently with 30 Hz contractions simultaneous BFR induced severe hypoxia reducing PmvO2lower than present for maximal (100 Hz) contractions. Low force electrical stimulation (EXER) induced muscle hypertrophy (6.2%, P < 0.01) whereas CONT or BFR did not. EXER+BFR also induced an increase in muscle mass (11.0%, P < 0.01), and significantly increased fiber cross sectional area in the superficial TA (P < 0.05). Phosphorylation of ribosomal protein S6 was enhanced by EXER+BFR as PGC-1α and GLUT4 protein levels. Fibronectin type III domain-containing protein 5 (FNDC5), COX4, MCT1, and cluster of differentiation 147 (CD147) increased with EXER. EXER+BFR significantly increased MCT1 expression than EXER. These data demonstrate that microvascular hypoxia during contractions is not essential for hypertrophy. However, hypoxia induced via BFR may potentiate the muscle hypertrophic response with an increased glucose transporter and mitochondrial biogenesis, which contributes to the pleiotropic effects of exercise training with BFR that culminate in an improved capacity for sustained exercise.
Surface electromyography (sEMG) is a popular research tool in sport and rehabilitation sciences. Common study designs include the comparison of sEMG amplitudes collected from different muscles as participants perform various exercises and techniques under different loads. Based on such comparisons, researchers attempt to draw conclusions concerning the neuro- and electrophysiological underpinning of force production and hypothesize about possible longitudinal adaptations, such as strength and hypertrophy. However, such conclusions are frequently unsubstantiated and unwarranted. Hence, the goal of this review is to discuss what can and cannot be inferred from comparative research designs as it pertains to both the acute and longitudinal outcomes. General methodological recommendations are made, gaps in the literature are identified, and lines for future research to help improve the applicability of sEMG are suggested.
The compound muscle action potential (M wave) has been commonly used to assess the peripheral properties of the neuromuscular system. More specifically, changes in the M-wave features are used to examine alterations in neuromuscular propagation that can occur during fatiguing contractions. The utility of the M wave is based on the assumption that impaired neuromuscular propagation results in a decrease in M-wave size. However, there remains controversy on whether the size of the M wave is increased or decreased during and/or after high-intensity exercise. The controversy partly arises from the fact that previous authors have considered the M wave as a whole, i.e., without analyzing separately its first and second phases. However, in a series of studies we have demonstrated that the first and second phases of the M wave behave in a different manner during and after fatiguing contractions. The present review is aimed at five main objectives: (1) to describe the mechanistic factors that determine the M-wave shape; (2) to analyze the various factors influencing M-wave properties; (3) to emphasize the need to analyze separately the first and second M-wave phases to adequately identify and interpret changes in muscle fiber membrane properties; (4) to advance the hypothesis that it is an increase (and not a decrease) of the M-wave first phase which reflects impaired sarcolemmal membrane excitability; and (5) to revisit the involvement of impaired sarcolemmal membrane excitability in the reduction of the force generating capacity.
Background
Low-load resistance training (< 50% of one-repetition maximum [1RM]) associated with blood-flow restriction (BFR-RT) has been thought to promote increases in muscle strength and mass. However, it remains unclear if the magnitude of these adaptations is similar to conventional high-load resistance training (> 65% 1RM; HL-RT). Objective
To compare the effects of HL- versus BFR-RT on muscle adaptations using a systematic review and meta-analysis procedure. Methods
Studies were identified via electronic databases based on the following inclusion criteria: (a) pre- and post-training assessment of muscular strength; (b) pre- and post-training assessment of muscle hypertrophy; (c) comparison of HL-RT vs. BFR-RT; (d) score ≥ 4 on PEDro scale; (e) means and standard deviations (or standard errors) are reported from absolute values or allow estimation from graphs. If this last criterion was not met, data were directly requested from the authors. ResultsThe main results showed higher increases in muscle strength for HL- as compared with BFR-RT, even when considering test specificity, absolute occlusion pressure, cuff width, and occlusion pressure prescription. Regarding the hypertrophic response, results revealed similar effects between HL- and BFR-RT, regardless of the absolute occlusion pressure, cuff width, and occlusion pressure prescription. Conclusions
Based on the present data, maximum muscle strength may be optimized by specific training methods (i.e., HL-RT) while both HL- and BFR-RT seem equally effective in increasing muscle mass. Importantly, BFR-RT is a valid and effective approach for increasing muscle strength in a wide spectrum of ages and physical capacity, although it may seem particularly of interest for those individuals with physical limitations to engage in HL-RT.
We aimed to evaluate the effects of low-load resistance exercise with blood flow restriction (BFR) on high-energy phosphate metabolism, intracellular pH, and oxygenation level in the skeletal muscle. Seven males performed low-load ankle plantar flexion exercise (120 repetitions, 30% of one-repetition maximum) with and without BFR (130% of systolic blood pressure) inside a magnetic resonance device. Inorganic phosphate (Pi)-to-phosphocreatine (PCr) ratio, intracellular pH, and tissue oxygenation index (TOI) in the medial gastrocnemius were determined using ³¹P-magnetic resonance spectroscopy and near-infrared spectroscopy before and during exercise. The Pi-to-PCr ratio significantly increased during exercise in both conditions, with the BFR-condition values significantly exceeding the control-condition values. The BFR and control conditions showed significantly decreased intracellular pH during exercise, with the BFR-condition values being significantly lower than the control-condition values. The TOI significantly decreased during both exercises, but the decreases in the BFR condition were significantly greater than those observed in the control condition. Low-load BFR exercise places greater metabolic stress (greater PCr depletion, lower intracellular pH, and lower oxygenation level) on an exercising muscle than low-load non-restricted exercise.
Context:
The combined effect of neuromuscular electrical muscle stimulation (NMES) and blood flow restriction (BFR) on muscle mass and strength has not been thoroughly investigated.
Objective:
To examine the effects of combined and independent BFR and a low-intensity NMES on skeletal muscle adaptation.
Design:
Exploratory Study.
Setting:
Laboratory.
Participants:
Twenty recreationally active subjects.
Main outcome measures:
Subjects had each leg randomly allocated to one of four possible intervention groups: 1) cyclic BFR alone 2) NMES alone 3) BFR+NMES (COMB), or 4) control (CON). Each leg was stimulated in its respective intervention group for 32 minutes, 4d/wk for six weeks. Mean differences in size (g) and isometric strength (kg), between week 0 and week 6, were calculated for each group.
Results:
Leg strength increased 32±19 kg in the COMB group, which differed from the 3±11kg change in the CON group (p=0.03). The isolated NMES and BFR groups revealed increases of 16±28kg and 18±17kg, respectively, but these did not statistically differ from the control, or one another. No alterations were statistically significant for leg size.
Conclusion:
Compared to a control that received no treatment, the novel combination of BFR and NMES led to increasing muscular strength of the knee extensors, but not muscle mass which had a large inter-individual variability in response.
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.
The force exerted by a muscle during a voluntary contraction depends on the number of motor units recruited for the action and the rates at which they discharge action potentials (rate coding). Over most of the operating range of a muscle, the nervous system controls muscle force by varying both motor unit recruitment and rate coding. Except at relatively low forces, however, the control of muscle force depends primarily on rate coding, especially during fast contractions. This review provides five examples of how the modulation of rate coding influences the force exerted by muscle during voluntary actions. The five examples comprise fast contractions, lengthening and shortening contractions, steady isometric contractions, fatiguing contractions, and contractions performed after a change in the daily level of physical activity.
NADPH oxidases (NOX) are important sources of reactive oxygen species (ROS) in skeletal muscle, being involved in excitation-contraction coupling. Thus, we aimed to investigate if NOX activity and expression in skeletal muscle are fiber type specific and the possible contribution of this difference to cellular oxidative stress. Oxygen consumption rate, NOX activity and mRNA levels, and the activity of catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD), as well as the reactive protein thiol levels, were measured in the soleus (SOL), red gastrocnemius (RG), and white gastrocnemius (WG) muscles of rats. RG showed higher oxygen consumption flow than SOL and WG, while SOL had higher oxygen consumption than WG. SOL showed higher NOX activity, as well as NOX2 and NOX4 mRNA levels, antioxidant enzymatic activities, and reactive protein thiol contents when compared to WG and RG. NOX activity and NOX4 mRNA levels as well as antioxidant enzymatic activities were higher in RG than in WG. Physical exercise increased NOX activity in SOL and RG, specifically NOX2 mRNA levels in RG and NOX4 mRNA levels in SOL. In conclusion, we demonstrated that NOX activity and expression differ according to the skeletal muscle fiber type, as well as antioxidant defense.
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.
During exercise, there is a progressive reduction in the ability to produce muscle forces. Processes within the nervous system, as well as within the muscles contribute to this fatigue. In addition to impaired function of the motor system, sensations associated with fatigue, and impairment of homeostasis can contribute to impairment of performance during exercise. This review discusses some of the neural changes that accompany exercise and the development of fatigue. The role of brain monoaminergic neurotransmitter systems in whole-body endurance performance is discussed, particularly with regard to exercise in hot environments. Next, fatigue-related alterations in the neuromuscular pathway are discussed in terms of changes in motor unit firing, motoneuron excitability and motor cortical excitability. These changes have mostly been investigated during single-limb isometric contractions. Finally, the small-diameter muscle afferents that increase firing with exercise and fatigue are discussed. These afferents have roles in cardiovascular and respiratory responses to exercise, and in impairment of exercise performance through interaction with the motor pathway, as well as providing sensations of muscle discomfort. Thus, changes at all levels of the nervous system including the brain, spinal cord, motor output, sensory input and autonomic function occur during exercise and fatigue. The mix of influences and the importance of their contribution varies with the type of exercise being performed.
The size principle states that motoneurones are recruited in a sequence that follows a size rule; small motoneurones are recruited before large ones. By extension, exceptions to the principle would be identified when that size order is reversed for motoneurones within a functional group. At first glance, and ignoring for the moment the exact meaning of motoneurone size, these notions appear unambiguous. Some uncertainty arises, however, as to the nature of the experimental observations that would be necessary and sufficient to demonstrate exceptions to the size principle. In addition, it is unclear whether any such exceptions should be regarded as important to our understanding of neuromotor operation or function.
Purpose:
Blood-flow restricted resistance exercise training (BFRE) is suggested to be effective in rehabilitation training, but more knowledge is required about its potential muscle damaging effects. Therefore, we investigated muscle-damaging effects of BFRE performed to failure and possible protective effects of previous bouts of BFRE or maximal eccentric exercise (ECC).
Methods:
Seventeen healthy young men were allocated into two groups completing two exercise bouts separated by 14 days. One group performed BFRE in both exercise bouts (BB). The other group performed ECC in the first and BFRE in the second bout. BFRE was performed to failure. Indicators of muscle damage were evaluated before and after exercise.
Results:
The first bout in the BB group led to decrements in maximum isometric torque, and increases in muscle soreness, muscle water retention, and serum muscle protein concentrations after exercise. These changes were comparable in magnitude and time course to what was observed after first bout ECC. An attenuated response was observed in the repeated exercise bout in both groups.
Conclusion:
We conclude that unaccustomed single-bout BFRE performed to failure induces significant muscle damage. Additionally, both ECC and BFRE can precondition against muscle damage induced by a subsequent bout of BFRE.
Phosphoenolpyruvate (PEP) generated from pyruvate is required for de novo synthesis of glycerol and glycogen in skeletal muscle. One possible pathway involves synthesis of PEP from the citric acid
cycle intermediates via PEP carboxykinase, whereas another could involve reversal of pyruvate kinase (PK). Earlier studies
have reported that reverse flux through PK can contribute carbon precursors for glycogen synthesis in muscle, but the physiological
importance of this pathway remains uncertain especially in the setting of high plasma glucose. In addition, although PEP is
a common intermediate for both glyconeogenesis and glyceroneogenesis, the importance of reverse PK in de novo glycerol synthesis has not been examined. Here we studied the contribution of reverse PK to synthesis of glycogen and the
glycerol moiety of acylglycerols in skeletal muscle of animals with high plasma glucose. Rats received a single intraperitoneal
bolus of glucose, glycerol, and lactate under a fed or fasted state. Only one of the three substrates was 13C-labeled in each experiment. After 3 h of normal awake activity, the animals were sacrificed, and the contribution from each
substrate to glycogen and the glycerol moiety of acylglycerols was evaluated. The fraction of 13C labeling in glycogen and the glycerol moiety exceeded the possible contribution from either plasma glucose or muscle oxaloacetate.
The reverse PK served as a common route for both glyconeogenesis and glyceroneogenesis in the skeletal muscle of rats with
high plasma glucose. The activity of pyruvate carboxylase was low in muscle, and no PEP carboxykinase activity was detected.
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.
to the editor: We are compelled to clarify some points made by Farina et al. ([1][1]). In a previous exchange of letters Farina et al. sought that we “decompose a set of synthetic surface EMG signals that we [Farina et al.] generate with a model” to provide a convincing validation of our sEMG
to the editor: The Letter by De Luca et al. ([2][1]) reiterates the arguments presented by them in a previous exchange ([1][2], [3][3]). The issue concerns how to validate a generic algorithm that purports to decompose a surface EMG signal into its constituent motor unit action potentials. De Luca
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.
Over the past three decades various algorithms used to decompose the electromyographic (EMG) signal into its constituent motor unit action potentials (MUAPs) have been reported. All are limited to decomposing EMG signals from isometric contraction. In this report we describe a successful approach at decomposing the surface electromyographic (sEMG) signal collected from cyclic (repeated concentric and eccentric) dynamic contractions during flexion/extension of the elbow and during gait. The increased signal complexity introduced by the changing shapes of the MUAPs due to relative movement of the electrodes and the lengthening/shortening of muscle fibers was managed by an incremental approach to enhancing our established algorithm for decomposing sEMG signals obtained from isometric contractions. We used machine-learning algorithms and time-varying MUAP shape discrimination to decompose the sEMG signal from an increasingly challenging sequence of pseudo-static and dynamic contractions. The accuracy of the decomposition results was assessed by two verification methods that have been independently evaluated. The firing instances of the motor units had an accuracy of approximately 90%, with a MUAP train yield as high as 25. Preliminary observations from the performance of motor units during cyclic contractions indicate that during repetitive dynamic contractions the control of motor units is governed by the same rules as those evidenced during isometric contractions. Modifications in the control properties of motoneuron firings reported by previous studies were not confirmed. Instead, our data demonstrate that the common drive and hierarchical recruitment of motor units are preserved during concentric and eccentric contractions.
Copyright © 2014, Journal of Neurophysiology.
The effects on muscle swelling were compared between low-load resistance exercise to exhaustion with (BFR) and without blood flow restriction (NBFR).
Ten young men [aged 27 (SD 5) years, standing height 1.74 (SD 0.05) m, body mass 70.3 (SD 4.3) kg] performed 20 % of one repetition maximal dumbbell curl exercise to exhaustion (four sets, rest intervals were 30 s for BFR and/or 3 min for NBFR, respectively). One arm was randomly chosen for BFR exercise and the other arm performed NBFR exercise. During the BFR exercise session, an elastic cuff was worn proximally on the testing arm at 160 mmHg. Electromyography (EMG) signals were recorded from surface electrodes placed on the biceps brachii muscle and analyzed for integrated EMG (iEMG). Biceps brachii muscle thickness (MTH) was measured using B-mode ultrasound.
The total number of exercise repetitions was greater (p < 0.01) in NBFR (221 ± 67 reps) than in BFR (111 ± 36 reps). During the exercise session, iEMG for biceps brachii muscles increased (p < 0.01) during BFR and NBFR (3.94 and 4.45 times of baseline value). Immediately after the exercise, MTH sharply increased (p < 0.01) with BFR and NBFR (1.21 and 1.20 times of baseline value). These results demonstrate that both BFR and NBFR exercises lead to pronounced muscle activation and muscle swelling.
Low-load resistance exercise to exhaustion is an effective method for promoting muscle swelling regardless of BFR. Furthermore, our data indicate that the increase in muscle swelling for both NBFR and BFR is maintained even 60 min after the exercise.
Group III and IV muscle afferents originating in exercising limb muscle play a significant role in the development of fatigue during exercise in humans. Feedback from these sensory neurons to the central nervous system (CNS) reflexively increases ventilation and central (cardiac output) and peripheral (limb blood flow) hemodynamic responses during exercise and thereby assures adequate muscle blood flow and O2 delivery. This response depicts a key factor in minimizing the rate of development of peripheral fatigue and in optimizing aerobic exercise capacity. On the other hand, the central projection of group III/IV muscle afferents impairs performance and limits the exercising human via its diminishing effect on the output from spinal motoneurons which decreases voluntary muscle activation (i.e. facilitates central fatigue). Accumulating evidence from recent animal studies suggests the existence of two subtypes of group III/IV muscle afferents. While one subtype only responds to physiological and innocuous levels of endogenous intramuscular metabolites (lactate, ATP, protons) associated with ?normal?, predominantly aerobic exercise, the other subtype only responds to higher and concurrently noxious levels of metabolites present in muscle during ischaemic contractions or following, for example, hypertonic saline infusions. This review discusses the mechanisms through which group III/IV muscle afferent feedback mediates both central and peripheral fatigue in exercising humans. We also briefly summarize accumulating evidence from recent animal and human studies documenting the existence of two subtypes of group III/IV muscle afferents and the relevance of this discovery for the interpretation of previous work and the design of future studies.
Low-load blood flow restricted (BFR) resistance exercise has been suggested to be as effective as moderate and high-load resistance training for increasing muscle size and strength. The purpose of the study was to evaluate the effects of 6 weeks of HL or low-load BFR resistance training on neuromuscular function, strength, and hypertrophy of the knee extensors. Eighteen participants aged 18-22 years old were randomized to one of three training groups: moderate load (ML: 70% of 1 repetition maximum [1-RM]); BFR (20% 1-RM with a vascular restriction set to ~180 mmHg); and a control group (CON) that did not exercise. Participants performed leg extension (LE) and leg press exercises 3 times per week for 6 weeks. Measurements of isometric torque, LE 1-RM, central activation, electrically evoked torque, and muscle volume of the knee extensors were obtained before and after training. Isometric peak torque did not change following the training (p = 0.13). LE 1-RM improved in the ML (34 ± 20%; d = 0.78) and BFR (14 ± 5%; d = 0.67) groups compared to the CON group (0.6 ± 8%; d = 0.09; time x group interaction p = 0.02). Muscle volume increased in the ML (5.6%; d = 0.19) and BFR groups (2.5%; d = 0.09) with no change in the CON group (time x group interaction p = 0.001). There were no changes in central activation and evoked torque in any groups following the training (p > 0.05). Strength and hypertrophy were evident following ML and BFR resistance training programs indicating that both modal-ities are effective, although ML training appears to be a more potent and efficient. Neuromuscular changes were not evident and warrant more research.
Despite full voluntary effort, neuromuscular activation of the quadriceps femoris muscle appears inhibited during slow concentric and eccentric contractions. Our aim was to compare neuromuscular activation during maximal voluntary concentric and eccentric quadriceps contractions, hypothesizing that inhibition of neuromuscular activation diminishes with resistance training. In 15 men, pretraining electromyographic activity of the quadriceps muscles [vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF)] was 17–36% lower during slow and fast (30 and 240°/s) eccentric and slow concentric contractions compared with fast concentric contractions. After 14 wk of heavy resistance training, neuromuscular inhibition was reduced for VL and VM and was completely removed for RF. Concurrently, electromyographic activity increased 21–52, 22–29, and 16–32% for VL, VM, and RF, respectively. In addition, median power frequency decreased for VL and RF. Eccentric quadriceps strength increased 15–17%, whereas slow and fast concentric strength increased 15 and 8%, respectively. Pre- and posttraining median power frequency did not differ between eccentric and concentric contractions. In conclusion, quadriceps motoneuron activation was lower during maximal voluntary eccentric and slow concentric contractions compared with during fast concentric contraction in untrained subjects, and, after heavy resistance training, this inhibition in neuromuscular activation was reduced.
Fatela, P, Reis, JF, Mendonca, GV, Freitas, T, Valamatos, MJ, Avela, J, and Mil-Homens, P. Acute neuromuscular adaptations in response to low-intensity blood flow restricted exercise and high-intensity resistance exercise: are there any differences? J Strength Cond Res 32(4): 902-910, 2018-Numerous studies have reported similar neuromuscular adaptations between low-intensity (LI) blood-flow restricted exercise (BFRE) and high-intensity (HI) resistance training. Unfortunately, none of these experimental designs individualized blood flow restriction (BFR) levels to each participant. Thus, their findings are difficult to interpret. We aimed at comparing the acute effects of LI BFR (80% of absolute vascular occlusion pressure) with LI non-BFR and HI training on muscle torque, activation, and neuromuscular fatigue. Ten men (23.8 ± 5.4 years) exercised at 20 and 75% of 1 repetition maximum with and without BFR (for LI). Blood flow restriction pressure was determined individually using resting blood-flow measurements. Torque was determined during maximal voluntary contractions (MVCs) at pre-exercise and postexercise time points. Surface electromyographic activity (root mean square [RMS] and median frequency [MF]) was recorded for the rectus femoris (RF) and vastus medialis (VM) muscles, before and after each session of training, during isometric contractions at 20% MVC. Torque decreased post-HI and LI BFR (-9.5 and -7.8%, respectively; p < 0.01), but not after LI non-BFR. The MF was reduced following HI training in the VM and the RF muscles (-5.3 and -12.5%, respectively; p ≤ 0.05). Conversely, the impact of LI BFR on reducing MF was limited to the RF muscle (-10.7%, p ≤ 0.05). Finally, when compared to all other conditions, RMS values were consistently higher during submaximal contractions performed after HI training (p ≤ 0.05). Thus, we conclude that, despite enhancing the acute magnitude of muscular activation and fatigue, LI BFR exercise exerts a less profound impact on neuromuscular function than HI resistance training.
We aimed to evaluate the effects of low-load resistance exercise with blood flow restriction (BFR) on high-energy phosphate metabolism, intracellular pH, and oxygenation level in the skeletal muscle. Seven males performed low-load ankle plantar flexion exercise (120 repetitions, 30% of one-repetition maximum) with and without BFR (130% of systolic blood pressure) inside a magnetic resonance device. Inorganic phosphate (Pi)-To-phosphocreatine (PCR) ratio, intracellular pH, and tissue oxygenation index (TOI) in the medial gastrocnemius were determined using 31P-magnetic resonance spectroscopy and near-infrared spectroscopy before and during exercise. The Pi-To-PCR ratio significantly increased during exercise in both conditions, with the BFR-condition values significantly exceeding the control-condition values. The BFR and control conditions showed significantly decreased intracellular pH during exercise, with the BFR-condition values being significantly lower than the control-condition values. The TOI significantly decreased during both exercises, but the decreases in the BFR condition were significantly greater than those observed in the control condition. Low-load BFR exercise places greater metabolic stress (greater PCR depletion, lower intracellular pH, and lower oxygenation level) on an exercising muscle than low-load non-restricted exercise.
Long-term heavy-load contractions decrease the relative amount of the myosin heavy chain (MHC) IIX isoform in human skeletal muscle, but the timing of the down regulation in the short term is unknown. Untrained subjects performed two resistance bouts, in two consecutive days, with one leg, the other leg serving as a control (age 24±1, n=5). Muscle biopsies were obtained in both legs before, immediately after, and 24, 54 and 96 hours after exercise. Serial cryosection analysis combined immunohistochemistry and ATPase histochemistry with In Situ hybridization to identify the distribution of MHC isoforms and their corresponding transcripts, enabling identification of transitional fibres. Fibres positive solely for MHC IIX mRNA decreased in the exercised leg throughout the study period. At 96 hours post exercise no fibres solely expressed MHC IIX mRNA. In contrast, the number of fibres expressing MHC IIA mRNA increased throughout the study period. The percentage of fibres expressing mRNA for MHC I was unchanged in both legs at all time-points. Pronounced depletion of glycogen in the MHC IIX fibres of the exercised leg verifies that the type IIX fibres were active during the heavy load contractions. Major mismatch between MHC at the mRNA and protein levels was only found in the fibres of the exercised leg. These data provide unequivocal in situ evidence of an immediate shutdown of the MHC IIX gene after resistance exercise. A further novel finding was that the silencing of the MHC IIX gene is sustained at least 4 days after removal of the stimulus. This article is protected by copyright. All rights reserved.
Background and objective
Low-load exercise training with blood flow restriction (BFR) can increase muscle strength and may offer an effective clinical musculoskeletal (MSK) rehabilitation tool. The aim of this review was to systematically analyse the evidence regarding the effectiveness of this novel training modality in clinical MSK rehabilitation.
Design
This is a systematic review and meta-analysis of peer-reviewed literature examining BFR training in clinical MSK rehabilitation (Research Registry; researchregistry91).
Data sources
A literature search was conducted across SPORTDiscus (EBSCO), PubMed and Science Direct databases, including the reference lists of relevant papers. Two independent reviewers extracted study characteristics and MSK and functional outcome measures. Study quality and reporting was assessed using the Tool for the assEssment of Study qualiTy and reporting in EXercise.
Eligibility
Search results were limited to exercise training studies investigating BFR training in clinical MSK rehabilitation, published in a scientific peer-reviewed journal in English.
Results
Twenty studies were eligible, including ACL reconstruction (n=3), knee osteoarthritis (n=3), older adults at risk of sarcopenia (n=13) and patients with sporadic inclusion body myositis (n=1). Analysis of pooled data indicated low-load BFR training had a moderate effect on increasing strength (Hedges’ g=0.523, 95% CI 0.263 to 0.784, p<0.001), but was less effective than heavy-load training (Hedges’ g=0.674, 95% CI 0.296 to 1.052, p<0.001).
Conclusion
Compared with low-load training, low-load BFR training is more effective, tolerable and therefore a potential clinical rehabilitation tool. There is a need for the development of an individualised approach to training prescription to minimise patient risk and increase effectiveness.
Introduction:
We recently developed an animal model to investigate the effects of eccentric contraction (ECC) and blood flow restriction (BFR) on muscle tissue at the cellular level. This study clarified the effects of repeated BFR, ECC, and BFR combined with ECC (BFR+ECC) on muscle fiber hypertrophy.
Methods:
Male Wistar rats were assigned to 3 groups: BFR, ECC, and BFR+ECC. The contralateral leg in the BFR group served as a control (CONT). Muscle fiber cross sectional area (CSA) of the tibialis anterior was determined after the respective treatments for 6 weeks.
Results:
CSA was greater in the BFR+ECC group than in the CONT (P?<?0.01) and ECC (P?<?0.05) groups. CSA was greater in the BFR group than that in the CONT group (P?<?0.05).
Discussion:
These results suggest that repeated BFR alone as well as BFR+ECC induces muscle fiber hypertrophy at the cellular level. This article is protected by copyright. All rights reserved.
Muscle fatigue can result from either the accumulation of metabolic by-products (e.g. Pi and H+) or a decrease in myoplasmic Ca++, however individually neither change can quantitatively explain the decrease in force capacity. Therefore, the emerging view is that, by decreasing the sensitivity of myofilaments to calcium, Pi and H+ act synergistically with decreased Ca++ levels to contribute to fatigue. SUMMARY: Skeletal muscle fatigue resulting from intense contractile activity is caused, in large part, by the synergistic action of increased metabolic by-products and reduced myoplasmic calcium.
to the editor: Enoka and Duchateau ([2][1]) correctly call for caution when interpreting voluntary surface electromyography (sEMG) in terms of neural drive. If voluntary sEMG signals recorded during nonfatiguing isometric contractions depend on the number of motor units recruited, their firing rate
Effects of low-intensity exercise (LIE) combined with or without heat-stress on muscle hypertrophy were investigated. Nine healthy men were subjected to 10 weeks of LIE for elbow flexor muscles {4 days/wk at less than 30 repetition maximum (RM), 3 sets (30 repetitions) of flexion-extension exercise of elbow joints}. The 60-min heat-stress was applied to only non-dominant arm, which performed LIE during the last 30-min period, by using a heat- and steam-generating sheet (heating area was set for 430 cm2, Kao Corporation, Tokyo, Japan). The dominant arm was subjected to only LIE. Maximum isometric force in flexion of the heated non-dominant, not the unheated dominant, arm significantly increased (18.4%) after 10-week LIE (p<0.05). However, the maximum isometric torque in extension of both arms was not improved. Mean cross-sectional area of biceps brachii muscles in the non-dominant, not the dominant, arm was significantly increased by LIE combined with heat-stress for 10 weeks (7.5%, p<0.05). It was strongly indicated that exercise training at an intensity even lower than 50% 1 RM could be effective in increasing of muscle strength associated with hypertrophy, when the training was combined with heating. These results suggest that heat-stress might be a useful countermeasure for prevention of muscular atrophy during space flight and/or long-term bed rest. Its application could be also extended to rehabilitation.
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.