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Blood Flow Restriction Training: A Tool to Enhance Rehabilitation and Build Athlete Resiliency
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The mammalian target of rapamycin (mTOR) is a protein kinase that controls cellular metabolism, catabolism, immune responses,autophagy, survival, proliferation, and migration, to maintain cellular homeostasis. The mTOR signaling cascade consists of twodistinct multi-subunit complexes named mTOR complex 1/2 (mTORC1/2). mTOR catalyzes the phosphorylation of several criticalproteins like AKT, protein kinase C, insulin growth factor receptor (IGF-1R), 4E binding protein 1 (4E-BP1), ribosomal protein S6kinase (S6K), transcription factor EB (TFEB), sterol-responsive element-binding proteins (SREBPs), Lipin-1, and Unc-51-likeautophagy-activating kinases. mTOR signaling plays a central role in regulating translation, lipid synthesis, nucleotide synthesis,biogenesis of lysosomes, nutrient sensing, and growth factor signaling. The emerging pieces of evidence have revealed that theconstitutive activation of the mTOR pathway due to mutations/amplification/deletion in either mTOR and its complexes (mTORC1and mTORC2) or upstream targets is responsible for aging, neurological diseases, and human malignancies. Here, we provide thedetailed structure of mTOR, its complexes, and the comprehensive role of upstream regulators, as well as downstream effectors ofmTOR signaling cascades in the metabolism, biogenesis of biomolecules, immune responses, and autophagy. Additionally, wesummarize the potential of long noncoding RNAs (lncRNAs) as an important modulator of mTOR signaling. Importantly, we havehighlighted the potential of mTOR signaling in aging, neurological disorders, human cancers, cancer stem cells, and drug resistance.Here, we discuss the developments for the therapeutic targeting of mTOR signaling with improved anticancer efficacy for thebenefit of cancer patients in clinics.
A BSTRACT
Aims
Pulmonary embolism (PE) is the most severe complication of deep venous thrombosis (DVT). This study was designed to evaluate the usefulness of modified Wells score combined with age-adjusted D-dimer cut-off levels as a clinical pre-test probability assessment for predicting PE in patients ‘at risk for DVT.’
Methods
This was a cross-sectional study including 200 in-patients at risk for DVT. Patients were categorized as ‘pulmonary embolism unlikely’ or ‘pulmonary embolism likely’ using modified Wells score and underwent D-dimer testing. PE was considered excluded in patients classified as unlikely with normal D-dimer levels, whereas the rest of the patients underwent computed tomography pulmonary angiogram (CTPA).
Results
Out of 200 patients, 163 patients (81.50%) were ‘pulmonary embolism unlikely,’ whereas 37 patients (18.50%) were ‘pulmonary embolism likely.’ Of 163 patients categorized as ‘pulmonary embolism unlikely,’ 67 patients (41.5%) had normal D-dimer values and were excluded from CTPA. PE was detected in 24.2% of the patients who underwent CTPA.
Conclusion
The combined strategy using modified Wells score and age-adjusted D-dimer cut-off value has 100% sensitivity and a negative predictive value and can be used to safely exclude PE in in-patients.
Total knee arthroplasty (TKA) is one of the most performed operations in the world, especially in the elderly. Aging has a significant effect on joint cartilage, muscle strength, and muscle mass. Following a TKA, despite the significant reduction of symptoms and the improvement in mobility, muscle strength and muscle mass recovery remains a significant challenge. Restrictions that arise from the surgical procedure include joint loading, functional activities, and range of motion, along with limitations related to the age of the individual and their previous loading history, these are the significant restrictions, at least in the early stages of rehabilitation. Evidence indicates that blood flow restriction (BFR) training has significant potential to enhance recovery via implementation of low-load or low-intensity exercise. While respecting the indications and contraindications related to BFR application, the optimization of metabolic stress seems to offer a bridging therapy to heavy load while reducing pain and inflammation. Thus, the combination of BFR and low loads may improve muscular recovery (strength and mass), and aerobic training protocols appear to show significant enhancement of multiple cardiopulmonary parameters. Mounting evidence, direct and indirect, indicate that BFR training may have the potential to benefit the pre-operative and post-operative TKA rehabilitation phases and enhance functional recovery and physical abilities in the elderly.
Background
Blood flow restriction combined with low load resistance training (LL-BFRT) is associated with increases in upper limb muscle strength and size. The effect of LL-BFRT on upper limb muscles located proximal to the BFR cuff application is unclear.
Objective
The aim of this systematic review was to evaluate the effect of LL-BFRT compared to low load, or high load resistance training (LL-RT, HL-RT) on musculature located proximal to cuff placement.
Methods
Six electronic databases were searched for randomized controlled trials (RCTs). Two reviewers independently evaluated the risk of bias using the PEDro scale. We performed a meta-analysis using a random effects model, or calculated mean differences (fixed-effect) where appropriate. We judged the certainty of evidence using the GRADE approach.
Results
The systematic literature searched yielded 346 articles, of which 9 studies were eligible. The evidence for all outcomes was of very low to low certainty. Across all comparisons, a significant increase in bench press and shoulder flexion strength was found in favor of LL-BFRT compared to LL-RT, and in shoulder lean mass and pectoralis major thickness in favor of the LL-BFRT compared to LL-RT and HL-RT, respectively. No significant differences were found between LL-BFRT and HL-RT in muscle strength.
Conclusion
With low certainty LL-BFRT appears to be equally effective to HL-RT for improving muscle strength in upper body muscles located proximal to the BFR stimulus in healthy adults. Furthermore, LL-BFRT may induce muscle size increase, but these adaptations are not superior to LL-RT or HL-RT.
Background:
Recent evidence indicates that combined upper extremity blood flow restriction (BFR, applied distally to the shoulder) and low-load resistance exercise (LIX) augments clinically meaningful responses in shoulder region tissues proximal to the occlusion site. The purpose of this investigation was to determine the efficacy of BFR-LIX for the shoulder when added to standard offseason training in Division IA collegiate baseball pitchers. We hypothesized that BFR-LIX would augment training-induced increases in shoulder-region lean mass, rotator cuff strength, and endurance. As secondary outcomes, we sought to explore the impact of BFR-LIX rotator cuff training on pitching mechanics.
Methods:
Twenty-eight collegiate baseball pitchers were randomized into 2 groups (BFRN=15, NOBFRN=13) that, in conjunction with offseason training, performed 8wks of shoulder LIX [Throwing arm only; 2/wk, 4 sets (30/15/15/fatigue), 20%isometric max] using 4 exercises [cable external and internal rotation (ER/IR), dumbbell scaption, and side-lying dumbbell ER]. The BFR group also trained with an automated tourniquet on the proximal arm (50%-occlusion). Regional lean mass (dual-energy x-ray absorptiometry), rotator cuff strength (dynamometry: IR0&90, ° ER0&90, ° Scaption, Flexion), and fastball biomechanics were assessed pre- and post-training. Achievable workload (sets × reps × resistance) was also recorded. An ANCOVA (covaried on baseline measures) repeated on training timepoint was used to detect within-group and between-group differences in outcome measures (α=0.05). For significant pairwise comparisons, effect size (ES) was calculated using a Cohen's d statistic and interpreted as: 0-0.1, negligible(N); 0.1-0.3, small(S); 0.3-0.5, moderate(M); 0.5-0.7, large(L); >0.7, very large(VL).
Results:
Following training, the BFR group experienced greater increases in shoulder-region lean mass [BFR: ↑227±60g, NOBFR: ↑75±37g, P=0.018, ES=1.0(VL)] and isometric strength for IR90° (↑2.4±2.3kg, P=0.041, ES=0.9VL). The NOBFR group experienced decreased shoulder flexion (↓1.6±0.8kg, P=0.007, ES=1.4VL) and IR at 0°(↓2.9±1.5kg, P=0.004, ES=1.1VL). The BFR group had a greater increase in achievable workload for the scaption exercise (BFR: ↑190±3.2kg, NOBFR: ↑90±3.3kg, P=0.005, ES=0.8VL). Only the NOBFR group was observed to experience changes in pitching mechanics following training with increased shoulder external rotation at lead foot contact (↑9.0°±7.9, P=0.028, ES=0.8VL) as well as reduced forward (↓3.6°±2.1, P=0.001, ES=1.2VL) and lateral (↓4.6°±3.4, P=0.007, ES=1.0VL) trunk tilt at ball release.
Conclusion:
BFR-LIX rotator cuff training performed in conjunction with a collegiate offseason program augments increases in shoulder lean mass as well as muscular endurance while maintaining rotator cuff strength and possibly pitching mechanics in a manner that may contribute to favorable outcomes and injury prevention in baseball pitching athletes.
Background
Traumatic shoulder instability is a common injury in athletes and military personnel. Surgical stabilization reduces recurrence, but athletes often return to sport before recovering upper extremity rotational strength and sport-specific abilities. Blood flow restriction (BFR) may stimulate muscle growth without the need for heavy resistance training post-surgically.
Hypothesis/Purpose
To observe changes in shoulder strength, self-reported function, upper extremity performance, and range of motion (ROM) in military cadets recovering from shoulder stabilization surgery who completed a standard rehabilitation program with six weeks of BFR training.
Study Design
Prospective case series
Methods
Military cadets who underwent shoulder stabilization surgery completed six weeks of upper extremity BFR training, beginning post-op week six. Primary outcomes were shoulder isometric strength and patient-reported function assessed at 6-weeks, 12-weeks, and 6-months postoperatively. Secondary outcomes included shoulder ROM assessed at each timepoint and the Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST), the Upper Extremity Y-Balance Test (UQYBT), and the Unilateral Seated Shotput Test (USPT) assessed at the six-month follow-up.
Results
Twenty cadets performed an average 10.9 BFR training sessions over six weeks. Statistically significant and clinically meaningful increases in surgical extremity external rotation strength ( p < 0.001; mean difference, .049; 95% CI: .021, .077), abduction strength ( p < 0.001; mean difference, .079; 95% CI: .050, .108), and internal rotation strength ( p < 0.001; mean difference, .060; CI: .028, .093) occurred from six to 12 weeks postoperatively. Statistically significant and clinically meaningful improvements were reported on the Single Assessment Numeric Evaluation ( p < 0.001; mean difference, 17.7; CI: 9.4, 25.9) and Shoulder Pain and Disability Index ( p < 0.001; mean difference, -31.1; CI: -44.2, -18.0) from six to 12 weeks postoperatively. Additionally, over 70 percent of participants met reference values on two to three performance tests at 6-months.
Conclusion
While the degree of improvement attributable to the addition of BFR is unknown, the clinically meaningful improvements in shoulder strength, self-reported function, and upper extremity performance warrant further exploration of BFR during upper extremity rehabilitation.
Level of Evidence
4, Case Series
Background:
Progressive overload is a principle of resistance training exercise program design that typically relies on increasing load to increase neuromuscular demand to facilitate further adaptations. However, little attention has been given to another way of increasing demand-increasing the number of repetitions.
Objective:
This study aimed to compare the effects of two resistance training programs: (1) increasing load while keeping repetition range constant vs (2) increasing repetitions while keeping load constant. We aimed to compare the effects of these programs on lower body muscle hypertrophy, muscle strength, and muscle endurance in resistance-trained individuals over an 8-week study period.
Methods:
Forty-three participants with at least 1 year of consistent lower body resistance training experience were randomly assigned to one of two experimental, parallel groups: A group that aimed to increase load while keeping repetitions constant (LOAD: n = 22; 13 men, nine women) or a group that aimed to increase repetitions while keeping load constant (REPS: n = 21; 14 men, seven women). Subjects performed four sets of four lower body exercises (back squat, leg extension, straight-leg calf raise, and seated calf raise) twice per week. We assessed one repetition maximum (1RM) in the Smith machine squat, muscular endurance in the leg extension, countermovement jump height, and muscle thickness along the quadriceps and calf muscles. Between-group effects were estimated using analyses of covariance, adjusted for pre-intervention scores and sex.
Results:
Rectus femoris growth modestly favored REPS (adjusted effect estimate (CI90%), sum of sites: 2.8 mm [-0.5, 5.8]). Alternatively, dynamic strength increases slightly favored LOAD (2.0 kg [-2.4, 7.8]), with differences of questionable practical significance. No other notable between-group differences were found across outcomes (muscle thicknesses, <1 mm; endurance, <1%; countermovement jump, 0.1 cm; body fat, <1%; leg segmental lean mass, 0.1 kg), with narrow CIs for most outcomes.
Conclusion:
Both progressions of repetitions and load appear to be viable strategies for enhancing muscular adaptations over an 8-week training cycle, which provides trainers and trainees with another promising approach to programming resistance training.
Background
Muscle atrophy is common after an injury to the knee and anterior cruciate ligament reconstruction (ACLR). Blood flow restriction therapy (BFR) combined with low-load resistance exercise may help mitigate muscle loss and improve the overall condition of the lower extremity (LE).
Purpose
To determine whether BFR decreases the loss of LE lean mass (LM), bone mass, and bone mineral density (BMD) while improving function compared with standard rehabilitation after ACLR.
Study Design
Randomized controlled clinical trial
Methods
A total of 32 patients undergoing ACLR with bone-patellar tendon-bone autograft were randomized into 2 groups (CONTROL: N = 15 [male = 7, female = 8; age = 24.1 ± 7.2 years; body mass index [BMI] = 26.9 ± 5.3 kg/m2] and BFR: N = 17 [male = 12, female = 5; age = 28.1 ± 7.4 years; BMI = 25.2 ± 2.8 kg/m2]) and performed 12 weeks of postsurgery rehabilitation with an average follow-up of 2.3 ± 1.0 years. Both groups performed the same rehabilitation protocol. During select exercises, the BFR group exercised under 80% arterial occlusion of the postoperative limb (Delfi tourniquet system). BMD, bone mass, and LM were measured using DEXA (iDXA, GE) at presurgery, week 6, and week 12 of rehabilitation. Functional measures were recorded at week 8 and week 12. Return to sport (RTS) was defined as the timepoint at which ACLR-specific objective functional testing was passed at physical therapy. A group-by-time analysis of covariance followed by a Tukey’s post hoc test were used to detect within- and between-group changes. Type I error; α = 0.05.
Results
Compared with presurgery, only the CONTROL group experienced decreases in LE-LM at week 6 (−0.61 ± 0.19 kg, −6.64 ± 1.86%; P < 0.01) and week 12 (−0.39 ± 0.15 kg, −4.67 ± 1.58%; P = 0.01) of rehabilitation. LE bone mass was decreased only in the CONTROL group at week 6 (−12.87 ± 3.02 g, −2.11 ± 0.47%; P < 0.01) and week 12 (−16.95 ± 4.32 g,−2.58 ± 0.64%; P < 0.01). Overall, loss of site-specific BMD was greater in the CONTROL group ( P < 0.05). Only the CONTROL group experienced reductions in proximal tibia (−8.00 ± 1.10%; P < 0.01) and proximal fibula (−15.0±2.50%, P < 0.01) at week 12 compared with presurgery measures. There were no complications. Functional measures were similar between groups. RTS time was reduced in the BFR group (6.4 ± 0.3 months) compared with the CONTROL group (8.3 ± 0.5 months; P = 0.01).
Conclusion
After ACLR, BFR may decrease muscle and bone loss for up to 12 weeks postoperatively and may improve time to RTS with functional outcomes comparable with those of standard rehabilitation.
This umbrella review aimed to analyze the different variables of resistance training and their effect on hypertrophy, and to provide practical recommendations for the prescription of resistance training programs to maximize hypertrophy responses. A systematic research was conducted through of PubMed/MEDLINE, SPORTDiscus and Web of Science following the preferred reporting items for systematic reviews and meta-analyses statement guidelines. A total of 52 meta-analyses were found, of which 14 met the inclusion criteria. These studies were published between 2009 and 2020 and comprised 178 primary studies corresponding to 4784 participants. Following a methodological quality analysis, nine meta-analyses were categorized as high quality, presenting values of 81-88%. The remaining meta-analyses were rated as moderate quality, with values between 63-75%. Based on this umbrella review, we can state that at least 10 sets per week per muscle group is optimal, that eccentric contractions seem important, very slow repetitions (≥10s) should be avoided, and that blood flow restriction might be beneficial for some individuals. In addition, other variables as, exercise order, time of the day and type of periodization appear not to directly influence the magnitude of muscle mass gains. These findings provide valuable information for the design and configuration of the resistance training program with the aim of optimizing muscle hypertrophy.
Objective: To identify current evidence on blood flow restriction training (BFRT) in tendon injuries and healthy tendons, evaluating physiological tendon effects, intervention parameters and outcomes.
Methods: This scoping review was reported in accordance with the PRISMA Extension for Scoping Reviews (PRISMA-ScR). Databases searched included MEDLINE, CINAHL, AMED, EMBase, SPORTDiscus, Cochrane library (Controlled trials, Systematic reviews), and five trial registries. Two independent reviewers screened studies at title/abstract and full text. Following screening, data was extracted and charted, and presented as figures and tables alongside a narrative synthesis. Any study design conducted on adults, investigating the effects of BFRT on healthy tendons or tendon pathology were included. Data were extracted on physiological tendon effects, and intervention parameters and outcomes with BFRT.
Results: 13 studies were included, 3 on tendinopathy, 2 on tendon ruptures and 8 on healthy Achilles, patellar, supraspinatus and vastus lateralis tendons. A variety of outcomes were assessed, including pain, function, strength, and tendon morphological and mechanical properties, particularly changes in tendon thickness. BFRT intervention parameters were heterogeneously prescribed.
Conclusion: Despite a dearth of studies to date on the effects of BFRT on healthy tendons and in tendon pathologies, preliminary evidence for beneficial effects of BFRT on tendons and clinical outcomes is encouraging. As BFRT is a relatively novel method, definitive conclusions, and recommendations on BFRT in tendon rehabilitation cannot be made at present, which should be addressed in future research, due to the potential therapeutic benefits highlighted in this review.
Blood flow restriction training (BFRT) is a modality with growing interest in the last decade and has been recognized as a critical tool in rehabilitation medicine, athletic and clinical populations. Besides its potential for positive benefits, BFRT has the capability to induce adverse responses. BFRT may evoke increased blood pressure, abnormal cardiovascular responses and impact vascular health. Furthermore, some important concerns with the use of BFRT exists for individuals with established cardiovascular disease (e.g., hypertension, diabetes mellitus, and chronic kidney disease patients). In addition, considering the potential risks of thrombosis promoted by BFRT in medically compromised populations, BFRT use warrants caution for patients that already display impaired blood coagulability, loss of antithrombotic mechanisms in the vessel wall, and stasis caused by immobility (e.g., COVID-19 patients, diabetes mellitus, hypertension, chronic kidney disease, cardiovascular disease, orthopedic post-surgery, anabolic steroid and ergogenic substance users, rheumatoid arthritis, and pregnant/postpartum women). To avoid untoward outcomes and ensure that BFRT is properly used, efficacy endpoints such as a questionnaire for risk stratification involving a review of the patient’s medical history, signs, and symptoms indicative of underlying pathology is strongly advised. Here we present a model for BFRT pre-participation screening to theoretically reduce risk by excluding people with comorbidities or medically complex histories that could unnecessarily heighten intra- and/or post-exercise occurrence of adverse events. We propose this risk stratification tool as a framework to allow clinicians to use their knowledge, skills and expertise to assess and manage any risks related to the delivery of an appropriate BFRT exercise program. The questionnaires for risk stratification are adapted to guide clinicians for the referral, assessment, and suggestion of other modalities/approaches if/when necessary. Finally, the risk stratification might serve as a guideline for clinical protocols and future randomized controlled trial studies.
Resistance-based blood flow restriction training (BFRT) improves skeletal muscle strength and size. Unlike heavy-load resistance training (HLRT), there is debate as to whether strength adaptations following BFRT interventions can be primarily attributed to concurrent muscle hypertrophy, as the magnitude of hypertrophy is often minor. The present study aimed to investigate the effect of 7 weeks of BFRT and HLRT on muscle strength and hypertrophy. The expression of protein growth markers from muscle biopsy samples was also measured. Male participants were allocated to moderately heavy-load training (HL; n = 9), low-load BFRT (LL + BFR; n = 8), or a control (CON; n = 9) group to control for the effect of time. HL and LL + BFR completed 21 training sessions (3 d.week⁻¹) comprising bilateral knee extension and knee flexion exercises (HL = 70% one-repetition maximum (1-RM), LL + BFR = 20% 1-RM + blood flow restriction). Bilateral knee extension and flexion 1-RM strength were assessed, and leg muscle CSA was measured via peripheral quantitative computed tomography. Protein growth markers were measured in vastus lateralis biopsy samples taken pre- and post the first and last training sessions. Biopsy samples were also taken from CON at the same time intervals as HL and LL + BFR. Knee extension 1-RM strength increased in HL (19%) and LL + BFR (19%) but not CON (2%; p < 0.05). Knee flexion 1-RM strength increased similarly between all groups, as did muscle CSA (50% femur length; HL = 2.2%, LL + BFR = 3.0%, CON = 2.1%; TIME main effects). 4E-BP1 (Thr37/46) phosphorylation was lower in HL and LL + BFR immediately post-exercise compared with CON in both sessions (p < 0.05). Expression of other growth markers was similar between groups (p > 0.05). Overall, BFRT and HLRT improved muscle strength and size similarly, with comparable changes in intramuscular protein growth marker expression, both acutely and chronically, suggesting the activation of similar anabolic pathways. However, the low magnitude of muscle hypertrophy was not significantly different to the non-training control suggesting that strength adaptation following 7 weeks of BFRT is not driven by hypertrophy, but rather neurological adaptation.
Blood flow restriction (BFR) is an expanding rehabilitation modality that uses a tourniquet to reduce arterial inflow and occlude venous outflow in the setting of resistance training or exercise. Initially, this technique was seen as a way to stimulate muscular development, but improved understanding of its physiologic benefits and mechanism of action has allowed for innovative clinical applications. BFR represents a way to decrease stress placed on the joints without compromising improvements in strength, whereas for postoperative, injured, or load-compromised individuals BFR represents a way to accelerate recovery and prevent atrophy. There is also growing evidence to suggest that it augments cardiovascular fitness and attenuates pain. The purpose of this review is to highlight the physiology and evidence behind the various applications of BFR, with a focus on postoperative rehabilitation. While much remains to be learned, it is clear that blood flow restriction therapy stimulates muscle hypertrophy via a synergistic response to metabolic stress and mechanical tension, with supplemental benefits on cardiovascular fitness and pain. New forms of BFR and expanding applications in postoperative patients and athletes hold promise for expedited recovery. Continued adherence to rehabilitation guidelines and exploration of BFRs physiology and various applications will help optimize its effect and prescription.
Level of Evidence
V, expert opinion.
The use of blood flow restriction (BFR) within rehabilitation is rapidly increasing as further research is performed elucidating purported benefits such as improved muscular strength and size, neuromuscular control, decreased pain, and increased bone mineral density. Interestingly, these benefits are not isolated to structures distal to the occlusive stimulus. Proximal gains are of high interest to rehabilitation professionals, especially those working with patients who are limited due to pain or postsurgical precautions. The review to follow will focus on current evidence and ongoing hypotheses regarding physiologic responses to BFR, current clinical applications, proximal responses to BFR training, potential practical applications for rehabilitation and injury prevention, and directions for future research. Interestingly, benefits have been found in musculature proximal to the occlusive stimulus, which may lend promise to a greater variety of patient populations and conditions. Furthermore, an increasing demand for BFR use in the sports world warrants further research for performance research and recovery.
Level of Evidence
Level V, expert opinion.
Category
Sports; Other
Introduction/Purpose
Blood flow restriction (BFR) therapy involves the use of a tourniquet to partially occlude blood flow to the affected limb, creating an anaerobic environment during exercise. This is thought to stimulate growth and recovery by increasing the body's anabolic response. BFR therapy can be initiated shortly after surgery since it allows for significant muscle activation with limited load bearing. To date, no existing study has evaluated the effect of using BFR therapy for recovery following Achilles tendon rupture and repair, after which patients often experience significant losses in calf strength and girth. This is a randomized controlled trial designed to study whether BFR can minimize loss of calf strength and muscle volume after Achilles rupture compared to a conventional physical therapy protocol.
Methods
Patients presenting with an acute Achilles tendon rupture were randomized into the BFR or control group. Patients in the control group performed at-home exercises and began in-person physical therapy at 6 weeks postoperatively, as is the standard of care in our practice. The exercises were standardized across groups with BFR the isolated variable. The primary outcome studied was ankle plantarflexion strength as measured during isokinetic strength testing 3 months after surgical repair. We also tested knee strength during flexion and extension. All strength tests were performed at two rotational speeds. Calf atrophy was assessed by measuring the circumference of both calves 15 cm below the joint line at the time of operation and at 2 weeks, 6 weeks, 3 months, and 6 months postoperatively. Finally, Patient-Reported Outcome Measurement Information System (PROMIS) scores were collected pre- and postoperatively.
Results
The study enrolled 43 patients, 24 of whom were assigned to the BFR group. 30 patients completed strength testing at 3 months and 26 at 6 months. Calf measurements through 3 months were completed for 39 patients and 6 month measurements were completed for 32 patients. Results for ankle plantarflexion strength at 3 months are displayed in Table 1, showing that patients in the BFR group demonstrated greater absolute strength in the operative calf compared to the control group, but no significant advantage in strength relative to the uninvolved calf. We failed to detect a significant difference in strength between groups for ankle dorsiflexion, knee extension, or knee flexion. Our model of calf circumference over time showed that BFR had a positive but insignificant correlation to calf circumference (p = 0.59). The only factors that demonstrated a significant (p<0.05) positive relationship to calf circumference were male sex and BMI.
Conclusion
We have observed significant advantages in the BFR group when analyzing absolute calf strength metrics when compared to a randomized control group. This indicates that, when used during rehabilitation following Achilles rupture, BFR therapy may increase the strength of the operative leg and may facilitate recovery and outcome.
Blood flow restriction (BFR) training is increasing in popularity in the fitness and rehabilitation settings due to its role in optimizing muscle mass and strength as well as cardiovascular capacity, function, and a host of other benefits. However, despite the interest in this area of research, there are likely some perceived barriers that practitioners must overcome to effectively implement this modality into practice. These barriers include determining appropriate BFR training pressures, access to appropriate BFR training technologies for relevant demographics based on the current evidence, a comprehensive and systematic approach to medical screening for safe practice and strategies to mitigate excessive perceptual demands of BFR training to foster long-term compliance. This manuscript attempts to discuss each of these barriers and provides evidence-based strategies and direction to guide clinical practice and future research.
Background:
Although blood flow restriction (BFR) is becoming increasingly popular in physical therapy and athletic training settings, little is known about the effects of BFR combined with low-intensity exercise (LIX) on muscles proximal to the site of occlusion.
Hypothesis/Purpose:
Determine whether LIX combined with BFR applied distally to the shoulder on the brachial region of the arm (BFR-LIX) promotes greater increases in shoulder lean mass, rotator cuff strength, endurance, and acute increases in shoulder muscle activation compared with LIX alone. We hypothesized that BFR-LIX would elicit greater increases in rotator cuff strength, endurance, and muscle mass. We also hypothesized that the application of BFR would increase EMG amplitude in the shoulder muscles during acute exercise.
Study Design:
Controlled laboratory study.
Methods:
32 healthy adults were randomized into 2 groups (BFR group, 13 men, 3 women; No-BFR group, 10 men, 6 women) who performed 8 weeks of shoulder LIX (2 times per week; 4 sets [30/15/15/fatigue]; 20% maximum) using common rotator cuff exercises (cable external rotation [ER], cable internal rotation [IR], dumbbell scaption, and side-lying dumbbell ER). The BFR group also trained with an automated tourniquet placed at the proximal arm (50% occlusion). Regional lean mass (dual-energy x-ray absorptiometry), isometric strength, and muscular endurance (repetitions to fatigue [RTF]; 20% maximum; with and without 50% occlusion) were measured before and after training. Electromyographic amplitude (EMGa) was recorded from target shoulder muscles during endurance testing. A mixed-model analysis of covariance (covaried on baseline measures) was used to detect within-group and between-group differences in primary outcome measures (α = .05).
Results:
The BFR group had greater increases in lean mass in the arm (mean ± 95% CI: BFR, 175 ± 54 g; No BFR, –17 ± 77 g; P < .01) and shoulder (mean ± 95% CI: BFR, 278 ± 90 g; No BFR, 96 ± 61 g; P < .01), isometric IR strength (mean ± 95% CI: BFR, 2.9 ± 1.3 kg; No BFR, 0.1 ± 1.3 kg; P < .01), single-set RTF volume (repetitions × resistance) for IR (~1.7- to 2.1-fold higher; P < .01), and weekly training volume (weeks 4, 6-8, ~5%-22%; P < .05). Acute occlusion (independent of group or timepoint) yielded increases in EMGa during RTF (~10%-20%; P < .05).
Conclusion:
Combined BFR-LIX may yield greater increases in shoulder and arm lean mass, strength, and muscular endurance compared with fatiguing LIX alone during rotator cuff exercises. These findings may be due, in part, to a greater activation of shoulder muscles while using BFR.
Clinical Relevance:
The present study demonstrates that BFR-LIX may be a suitable candidate for augmenting preventive training or rehabilitation outcomes for the shoulder.
AJSM PODCAST DISCUSSION: http://sageorthopaedics.sage-publications.libsynpro.com/ajsm-august-2021-podcast-blood-flow-restriction-training-for-the-shoulder-a-case-for-proximal-benefit
The manipulation of blood flow in conjunction with skeletal muscle contraction has greatly informed the physiological understanding of muscle fatigue, blood pressure reflexes, and metabolism in humans. Recent interest in using intentional blood flow restriction (BFR) has focused on elucidating how exercise during periods of reduced blood flow affects typical training adaptations. A large initial appeal for BFR-training was driven by studies demonstrating rapid increases in muscle size, strength, and endurance capacity; even when notably low intensities and resistances, that would typically be incapable of stimulating change in healthy populations, were used. The incorporation of BFR-exercise into the training of strength- and endurance-trained athletes has recently been shown to provide additive training effects that augment skeletal muscle and cardiovascular adaptations. Recent observations suggest BFR-exercise alters acute physiological stressors such as local muscle oxygen availability and vascular shear-stress, which may lead to adaptations that are not easily attained with conventional training. This review explores these concepts and summarizes both the evidence-base and knowledge gaps regarding the application of BFR-training for athletes.
Loading recommendations for resistance training are typically prescribed along what has come to be known as the “repetition continuum”, which proposes that the number of repetitions performed at a given magnitude of load will result in specific adaptations. Specifically, the theory postulates that heavy load training optimizes increases maximal strength, moderate load training optimizes increases muscle hypertrophy, and low-load training optimizes increases local muscular endurance. However, despite the widespread acceptance of this theory, current research fails to support some of its underlying presumptions. Based on the emerging evidence, we propose a new paradigm whereby muscular adaptations can be obtained, and in some cases optimized, across a wide spectrum of loading zones. The nuances and implications of this paradigm are discussed herein.
Insulin-like growth factor-1 (IGF-1) is a key growth factor that regulates both anabolic and catabolic pathways in skeletal muscle. IGF-1 increases skeletal muscle protein synthesis via PI3K/Akt/mTOR and PI3K/Akt/GSK3β pathways. PI3K/Akt can also inhibit FoxOs and suppress transcription of E3 ubiquitin ligases that regulate ubiquitin proteasome system (UPS)-mediated protein degradation. Autophagy is likely inhibited by IGF-1 via mTOR and FoxO signaling, although the contribution of autophagy regulation in IGF-1-mediated inhibition of skeletal muscle atrophy remains to be determined. Evidence has suggested that IGF-1/Akt can inhibit muscle atrophy-inducing cytokine and myostatin signaling via inhibition of the NF-κΒ and Smad pathways, respectively. Several miRNAs have been found to regulate IGF-1 signaling in skeletal muscle, and these miRs are likely regulated in different pathological conditions and contribute to the development of muscle atrophy. IGF-1 also potentiates skeletal muscle regeneration via activation of skeletal muscle stem (satellite) cells, which may contribute to muscle hypertrophy and/or inhibit atrophy. Importantly, IGF-1 levels and IGF-1R downstream signaling are suppressed in many chronic disease conditions and likely result in muscle atrophy via the combined effects of altered protein synthesis, UPS activity, autophagy, and muscle regeneration.
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.
Wilk, M, Krzysztofik, M, Filip, A, Zajac, A, Bogdanis, GC, and Lockie, RG. Short-term blood flow restriction increases power output and bar velocity during the bench press. J Strength Cond Res XX(X): 000–000, 2020—This study examined the effect of blood flow restriction (BFR) with 2 different types of cuffs on peak power output (PP), mean power output (MP), peak bar velocity (PV), and mean bar velocity (MV) in the bench press exercise (BP). Fourteen healthy strength-trained male athletes (age = 27.6 ± 3.5 years; body mass = 84.1 ± 8.0 kg; height = 175.8 ± 6.7 cm; BP 1 repetition maximum [RM] = 138.6 ± 17.8 kg) performed 3 different testing protocols as follows: without BFR (NO-BFR), BFR with a narrow cuff (BFRNARROW), and BFR with a wide cuff (BFRWIDE) in a randomized crossover design. During all sessions, subjects performed one set of 3 repetitions of the BP exercise using 70% 1RM. Cuff pressure was set to approximately 90% full arterial occlusion pressure of the upper limb at rest. Analyses of variance showed an increase in PP (by 21%, p < 0.01; effect size [ES] = 1.67), MP (by 16%, p < 0.01; ES = 0.93), PV (by 22%, p < 0.01; ES = 1.79), and MV (by 21%, p < 0.01; ES = 1.36) during BFRWIDE compared with NO-BFR and a significant increase in PP (by 15%, p < 0.01; ES = 1.07), MP (by 17%, p < 0.01; ES = 0.78), PV (by 18%, p < 0.01; ES = 1.65), and MV (by 13% p < 0.01; ES = 1.00) during BFRWIDE compared with BFRNARROW. There were no significant differences in any of the variable between NO-BFR and BFRNARROW. The results of the study indicate that short-term BFR training increases power output and bar velocity during the BP exercise. However, only BFRWIDE significantly influenced bar velocity and power output, which indicates that the width of the cuff is a critical factor determining acute exercise adaptation during BFR resistance training.
Aim:
To investigate if short-term block-structured training consisting of alternating weeks of blood-flow restricted low-load resistance training (BFR-RT) and conventional free-flow heavy-load resistance training (HL-RT) leads to superior gains in mechanical muscle function, myofiber size and satellite cell (SC) content and myonuclear number compared to HL-RT alone.
Methods:
Eighteen active young participants (females/males: 5/13, 23±1.2yrs) were randomized to 6-weeks (22 sessions) of lower limb HL-RT (70-90% 1-RM) (HRT, n= 9) or block-structured training alternating weekly between BFR-RT (20% 1-RM) and HL-RT (BFR-HRT, n= 9). Maximal isometric knee extensor strength (MVC) and muscle biopsies(VL)were obtained pre and post training to examine changes in muscle strength, myofiber cross-sectional area (CSA), myonuclear (MN) number and satellite cell (SC) content.
Results:
MVC increased in both training groups (BFR-HRT: +12%, HRT: +7%; P< 0.05). Type II myofiber CSA increased similarly (+16%) in BFR-HRT and HRT (P< 0.05) while gains in type I CSA were observed following HRT only (+12%, P< 0.05). In addition, myonuclear number remained unchanged, whereas SC content increased in type II myofibers following HRT (+59%, P< 0.05).
Conclusions:
Short-term alternating BFR-RT and HL-RT did not produce superior gains in muscle strength or myofiber size compared to HL-RT alone. Noticeably however, conventional HL-RT could be periodically replaced by low-load BFR-RT without compromising training-induced gains in maximal muscle strength and type II myofiber size, respectively.
Background:
Exercise training (ET) with blood flow restriction (BFR) is becoming increasingly popular, but the majority of BFR ET studies have evaluated skeletal muscle strength and hypertrophy. The favorable effect of BFR ET on skeletal muscle and the vasculature appears to improve aerobic capacity (AC) although conflicting results have been observed.Purpose: The purposes of this systematic review with meta- analysis were to examine the effects of aerobic ET with and without BFR on AC and to compare the effect of low-to-moderate aerobic ET with and without BFR to high-intensity aerobic ET with and without BFR on AC.
Study design:
Systematic Review with Meta-analysis.
Methods:
A comprehensive search for studies examining the effects of aerobic ET with and without BFR on AC was performed. Inclusion criteria were: (a) the study was conducted in healthy individuals, (b) there was random allocation of study participants to training and control groups, (c) BFR was the sole intervention difference between the groups.
Results:
A total of seven studies (5 low-to-moderate ET and 2 high-intensity ET) were included in the meta-analysis providing data from 121 subjects. There was a significant standardized mean difference (SMD) of 0.38 (95% CI = 0.01, 0.75) in AC between the BFR and non-BFR groups of all seven studies (z = 2.01; p = 0.04). Separate analyses of the five low-to-moderate aerobic ET studies found similar results with aerobic ET with BFR eliciting a significantly greater AC (z = 2.47; p=0.01) than aerobic ET without BFR (SMD of 0.57; 95% CI = 0.12, 1.01). Separate analyses of the two high-intensity aerobic ET studies with and without BFR found no significant difference in AC between the groups (SMD of - 0.01; 95% CI = - 0.67, 0.64).
Conclusion:
Aerobic ET with BFR elicits a significantly greater AC than aerobic ET without BFR in healthy young adults. However, low-to-moderate intensity aerobic ET with BFR elicited a greater improvement in AC than aerobic ET without BFR while high-intensity aerobic ET with BFR did not elicit an improvement in AC over high-intensity aerobic ET without BFR.
Level of evidence:
1a.
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.
Background:
Effective hypertrophy-oriented resistance training (RT) should comprise a combination of mechanical tension and metabolic stress. Regarding training variables, the most effective values are widely described in the literature. However, there is still a lack of consensus regarding the efficiency of advanced RT techniques and methods in comparison to traditional approaches.
Methods:
MEDLINE and SPORTDiscus databases were searched from 1996 to September 2019 for all studies investigating the effects of advanced RT techniques and methods on muscle hypertrophy and training variables. Thirty articles met the inclusion criteria and were consequently included for the quality assessment and data extraction.
Results:
Concerning the time-efficiency of training, the use of agonist-antagonist, upper-lower body supersets, drop and cluster sets, sarcoplasma stimulating training, employment of fast, but controlled duration of eccentric contractions (~2s), and high-load RT supplemented with low-load RT under blood flow restriction may provide an additional stimulus and an advantage to traditional training protocols. With regard to the higher degree of mechanical tension, the use of accentuated eccentric loading in RT should be considered. Implementation of drop sets, sarcoplasma stimulating training, low-load RT in conjunction with low-load RT under blood flow restriction could provide time-efficient solutions to increased metabolic stress.
Conclusions:
Due to insufficient evidence, it is difficult to provide specific guidelines for volume, intensity of effort, and frequency of previously mentioned RT techniques and methods. However, well-trained athletes may integrate advanced RT techniques and methods into their routines as an additional stimulus to break through plateaus and to prevent training monotony.
Blood flow restriction (BFR) has been shown to produce beneficial adaptations to skeletal muscle. These adaptations have been documented in the civilian and military populations. BFR therapy may provide patients a safe method to begin strength training at earlier stages of rehabilitation to allow for earlier and more effective return to activity and improved military readiness. The purpose was to review BFR therapy physiology, complications, side effects, standardized treatment algorithms, and long-term patient outcomes.
Background
We implemented a blood flow restriction resistance training (BFR-RT) intervention during an 8-week rehabilitation programme in anterior cruciate ligament reconstruction (ACLR) patients within a National Health Service setting.
Objective
To compare the effectiveness of BFR-RT and standard-care traditional heavy-load resistance training (HL-RT) at improving skeletal muscle hypertrophy and strength, physical function, pain and effusion in ACLR patients following surgery.
Methods
28 patients scheduled for unilateral ACLR surgery with hamstring autograft were recruited for this parallel-group, two-arm, single-assessor blinded, randomised clinical trial following appropriate power analysis. Following surgery, a criteria-driven approach to rehabilitation was utilised and participants were block randomised to either HL-RT at 70% repetition maximum (1RM) (n = 14) or BFR-RT (n = 14) at 30% 1RM. Participants completed 8 weeks of biweekly unilateral leg press training on both limbs, totalling 16 sessions, alongside standard hospital rehabilitation. Resistance exercise protocols were designed consistent with standard recommended protocols for each type of exercise. Scaled maximal isotonic strength (10RM), muscle morphology of the vastus lateralis of the injured limb, self-reported function, Y-balance test performance and knee joint pain, effusion and range of motion (ROM) were assessed at pre-surgery, post-surgery, mid-training and post-training. Knee joint laxity and scaled maximal isokinetic knee extension and flexion strength at 60°/s, 150°/s and 300°/s were measured at pre-surgery and post-training.
Results
Four participants were lost, with 24 participants completing the study (12 per group). There were no adverse events or differences between groups for any baseline anthropometric variable or pre- to post-surgery change in any outcome measure. Scaled 10RM strength significantly increased in the injured limb (104 ± 30% and 106 ± 43%) and non-injured limb (33 ± 13% and 39 ± 17%) with BFR-RT and HL-RT, respectively, with no group differences. Significant increases in knee extension and flexion peak torque were observed at all speeds in the non-injured limb with no group differences. Significantly greater attenuation of knee extensor peak torque loss at 150°/s and 300°/s and knee flexor torque loss at all speeds was observed with BFR-RT. No group differences in knee extensor peak torque loss were found at 60°/s. Significant and comparable increases in muscle thickness (5.8 ± 0.2% and 6.7 ± 0.3%) and pennation angle (4.1 ± 0.3% and 3.4 ± 0.1%) were observed with BFR-RT and HL-RT, respectively, with no group differences. No significant changes in fascicle length were observed. Significantly greater and clinically important increases in several measures of self-reported function (50–218 ± 48% vs. 35–152 ± 56%), Y-balance performance (18–59 ± 22% vs. 18–33 ± 19%), ROM (78 ± 22% vs. 48 ± 13%) and reductions in knee joint pain (67 ± 15% vs. 39 ± 12%) and effusion (6 ± 2% vs. 2 ± 2%) were observed with BFR-RT compared to HL-RT, respectively.
Conclusion
BFR-RT can improve skeletal muscle hypertrophy and strength to a similar extent to HL-RT with a greater reduction in knee joint pain and effusion, leading to greater overall improvements in physical function. Therefore, BFR-RT may be more appropriate for early rehabilitation in ACLR patient populations within the National Health Service.
Key points
Performing resistance exercise with heavier loads is often proposed to be necessary for the recruitment of larger motor units and activation of type II muscle fibres, leading to type II fibre hypertrophy. Indirect measures [surface electromyography (EMG)] have been used to support this thesis, although we propose that lighter loads lifted to task failure (i.e. volitional fatigue) result in the similar activation of type II fibres.
In the present study, participants performed resistance exercise to task failure with heavier and lighter loads with both a normal and longer repetition duration (i.e. time under tension).
Type I and type II muscle fibre glycogen depletion was determined by neither load, nor repetition duration during resistance exercise performed to task failure.
Surface EMG amplitude was not related to muscle fibre glycogen depletion or anabolic signalling; however, muscle fibre glycogen depletion and anabolic signalling were related.
Performing resistance exercise to task failure, regardless of load lifted or repetition duration, necessitates the activation of type II muscle fibres.
Abstract
Heavier loads (>60% of maximal strength) are considered to be necessary during resistance exercise (RE) to activate and stimulate hypertrophy of type II fibres. Support for this proposition comes from observation of higher surface electromyography (EMG) amplitudes during RE when lifting heavier vs. lighter loads. We aimed to determine the effect of RE, to task failure, with heavier vs. lighter loads and shorter or longer repetition durations on: EMG‐derived variables, muscle fibre activation, and anabolic signalling. Ten recreationally‐trained young men performed four unilateral RE conditions randomly on two occasions (two conditions, one per leg per visit). Muscle biopsies were taken from the vastus lateralis before and one hour after RE. Broadly, total time under load, number of repetitions, exercise volume, EMG amplitude (at the beginning and end of each set) and total EMG activity were significantly different between conditions (P < 0.05); however, neither glycogen depletion (in both type I and type II fibres), nor phosphorylation of relevant signalling proteins showed any difference between conditions. We conclude that muscle fibre activation and subsequent anabolic signalling are independent of load, repetition duration and surface EMG amplitude when RE is performed to task failure. The results of the present study provide evidence indicating that type I and type II fibres are activated when heavier and lighter loads are lifted to task failure. We propose that our results explain why RE training with higher or lower loads, when loads are lifted to task failure, leads to equivalent muscle hypertrophy and occurs in both type I and type II fibres.
Purpose
To investigate whether blood flow restriction (BFR) without concomitant exercise mitigated strength reduction and atrophy of thigh muscles in participants under immobilization for lower limbs.
Methods
The following databases were searched: PubMed, CINAHL, PEDro, Web of Science, Central, and Scopus.
Results
The search identified 3 eligible studies, and the total sample in the identified studies consisted of 38 participants. Isokinetic and isometric torque of the knee flexors and extensors was examined in 2 studies. Cross-sectional area of thigh muscles was evaluated in 1 study, and thigh girth was measured in 2 studies. The BFR protocol was 5 sets of 5 min of occlusion and 3 min of free flow, twice daily for approximately 2 weeks. As a whole, the included studies indicate that BFR without exercise is able to minimize strength reduction and muscular atrophy after immobilization. It is crucial to emphasize, however, that the included studies showed a high risk of bias, especially regarding allocation concealment, blinding of outcome assessment, intention-to-treat analyses, and group similarity at baseline.
Conclusion
Although potentially useful, the high risk of bias presented by original studies limits the indication of BFR without concomitant exercise as an effective countermeasure against strength reduction and atrophy mediated by immobilization.
The current manuscript sets out a position stand for blood flow restriction exercise, focusing on the methodology, application and safety of this mode of training. With the emergence of this technique and the wide variety of applications within the literature, the aim of this position stand is to set out a current research informed guide to blood flow restriction training to practitioners. This covers the use of blood flow restriction to enhance muscular strength and hypertrophy via training with resistance and aerobic exercise and preventing muscle atrophy using the technique passively. The authorship team for this article was selected from the researchers focused in blood flow restriction training research with expertise in exercise science, strength and conditioning and sports medicine.
The purpose of this study was to compare the standing lower extremity limb occlusion pressure (LOP) between two units. It was hypothesized that the Delfi unit, which utilizes a wider cuff (11.5 cm), would require significantly less LOP as compared to the KAASTU unit, which utilizes a narrow cuff (5 cm). Twenty-nine healthy participants (22 men, 7 women) mean age 24 years old (± 1.7 SD) volunteered. The procedure was identical for each cuff, completed with 5 minutes of rest in between. The cuff was placed on the proximal left thigh in the standing position. The initial pressure was set to 50 mmHg and then increased in 50 mmHg increments until complete arterial occlusion was achieved or the unit went to its maximum pressure. Arterial blood flow was determined by a mobile ultrasound measured at the left popliteal artery. Paired samples t-tests were used to determine differences in LOP (mmHg) between the Delfi and KAATSU unit cuffs. Significant differences were observed between the cuffs (wide: 239.4 mmHg vs. narrow: 500 mmHg; p < 0.001). We were able to achieve complete arterial occlusion with the wide cuff. The KAATSU unit reached maximum pressure with all participants, therefore we were unable to achieve complete arterial occlusion with the narrow cuff. Although achieving complete arterial occlusion is not indicated or safe for BFR training, relative pressures are used and determined as a percentage of LOP. Our study found that the relative pressure of the wide cuff is lower than the narrow cuff.
Brief moments of blood flow occlusion followed by reperfusion may promote enhancements in exercise performance. Thus, this study assessed the 24-h effect of post-exercise ischemic conditioning (PEIC) on exercise performance and physiological variables in trained cyclists. In a randomized, single-blind study, 28 trained cyclists (27.1 ± 1.4 years) performed a maximal incremental cycling test (MICT). The outcome measures were creatine kinase (CK), muscle soreness and perceived recovery status, heart rate, perceived exertion and power output. Immediately after the MICT, the cyclists performed 1 of the following 4 interventions: 2 sessions of 5-min occlusion/5-min reperfusion (PEIC or SHAM, 2 x 5) or 5 sessions of 2-min occlusion/2-min reperfusion (PEIC or SHAM, 5 x 2). The PEIC (50 mm Hg above the systolic blood pressure) or SHAM (20 mm Hg) treatment was applied unilaterally on alternating thighs. At 24 h after the interventions, a second MICT was performed. In all the groups, the CK levels were increased compared with the baseline (p < 0.05) after the 24-h MICT. The PEIC groups (2 x 5 and 5 x 2) felt more tired at 24 h post intervention (p < 0.05). However, both PEIC groups maintained their performance (2 x 5: p = 0.819; 5 x 2: p = 0.790), while the SHAM groups exhibited decreased performance at 24 h post intervention compared to baseline (2 x 5: p = 0.015; 5 x 2: p = 0.045). A decrease in the maximal heart rate (HR) was found only in the SHAM 2 x 5 group (p = 0.015). There were no other significant differences in the heart rate, power output or perceived exertion after 24 h compared with the baseline values for any of the interventions (p > 0.05). In conclusion, PEIC led to maintained exercise performance 24 h post intervention in trained cyclists.
Background
The combination of low-load resistance training with blood flow restriction (BFR) has recently been shown to promote muscular adaptations in various populations. To date, however, evidence is sparse on how this training regimen influences muscle mass and strength in older adults.
Purpose
The purpose of this systematic review and meta-analysis was to quantitatively identify the effects of low-load BFR (LL-BFR) training on muscle mass and strength in older individuals in comparison with conventional resistance training programmes. Additionally, the effectiveness of walking with and without BFR was assessed.
Methods
A PRISMA-compliant systematic review and meta-analysis was conducted. The systematic literature research was performed in the following electronic databases from inception to 1 June 2018: PubMed, Web of Science, Scopus, CINAHL, SPORTDiscus and CENTRAL. Subsequently, a random-effects meta-analysis with inverse variance weighting was conducted.
Results
A total of 2658 articles were screened, and 11 studies with a total population of N = 238 were included in the meta-analysis. Our results revealed that during both low-load training and walking, the addition of BFR elicits significantly greater improvements in muscular strength with pooled effect sizes (ES) of 2.16 (95% CI 1.61 to 2.70) and 3.09 (95% CI 2.04 to 4.14), respectively. Muscle mass was also increased when comparing walking with and without BFR [ES 1.82 (95% CI 1.32 to 2.32)]. In comparison with high-load training, LL-BFR promotes similar muscle hypertrophy [ES 0.21 (95% CI − 0.14 to 0.56)] but lower strength gains [ES − 0.42 (95% CI − 0.70 to − 0.14)].
Conclusion
This systematic review and meta-analysis reveals that LL-BFR and walking with BFR is an effective interventional approach to stimulate muscle hypertrophy and strength gains in older populations. As BFR literature is still scarce with regard to potential moderator variables (e.g. sex, cuff pressure or training volume/frequency), further research is needed for strengthening the evidence for an effective application of LL-BFR training in older people.
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.
OBJECTIVE: To evaluate the effect of low-load resistance training with blood flow restriction (LLRT-BFR) when compared to LLRT with sham-BFR in patients with lateral elbow tendinopathy (LET).
DESIGN: Randomized controlled trial.
METHODS: Forty-six patients with LET were randomly assigned to a LLRT-BFR or a LLRT with sham-BFR treatment group. All patients received soft tissue massage, supervised exercises with BFR or sham intervention (twice a week for 6 weeks), advice, and a home exercise program. The primary outcome measures were pain intensity, patient-rated tennis elbow evaluation (PRTEE) score, pain-free grip strength, and global rating of change, measured at baseline, 6 weeks, and 12 weeks. Between-group differences were evaluated using mixed-effects models with participant-specific random effects for continuous data. Global rating of change was analyzed using logistic regression.
RESULTS: Statistically significant between-group differences were found in favor of LLRT-BFR compared to LLRT with sham-BFR in pain intensity at 12-week follow-up (−1.54, 95% CI: −2.89 to −0.18; P = .026), pain-free grip strength ratio at 6-week follow-up (0.20, 95% CI: 0.06 to 0.34; P = .005), and PRTEE at 6- and 12-week follow-up (−11.92, 95% CI: −20.26 to −3.59; P = .006, and −15.23, 95% CI: −23.57 to −6.9; P<.001, respectively). At 6- and 12-weeks, patients in the LLRT-BFR group had greater odds of reporting complete recovery or significant improvement (OR = 6.0, OR = 4.09, respectively).
CONCLUSION: Low-load resistance training with blood flow restriction produced significantly better results compared to the LLRT with sham-BFR for all primary outcomes. Considering the clinically significant between-group improvement in function (>11 points in PRTEE) and the better success rates in the LLRT-BFR group, this intervention may improve recovery in LET. J Orthop Sports Phys Ther 2022;52(12):803–825. Epub: 14 September 2022. doi:10.2519/jospt.2022.11211
The main goal of musculoskeletal rehabilitation is to achieve the pre-injury and/or pre-surgical physical function level with a low risk of re-injury. Blood flow restriction (BFR) training is a promising alternative to conventional therapy approaches during musculoskeletal rehabilitation because various studies support its beneficial effects on muscle mass, strength, aerobic capacity, and pain perception. In this perspective article, we used an evidence-based progressive model of a rehabilitative program that integrated BFR in four rehabilitation phases: (1) passive BFR, (2) BFR combined with aerobic training, (3) BFR combined with low-load resistance training, and (4) BFR combined with low-load resistance training and traditional high-load resistance training. Considering the current research, we suppose that a BFR-assisted rehabilitation has the potential to shorten the time course of therapy to reach the stage where the patient is able to tolerate resistance training with high loads. The information and arguments presented are intended to stimulate future research, which compares the time to achieve rehabilitative milestones and their physiological bases in each stage of the musculoskeletal rehabilitation process. This requires the quantification of BFR training-induced adaptations (eg, muscle mass, strength, capillary-to-muscle-area ratio, hypoalgesia, molecular changes) and the associated changes in performance with a high measurement frequency (≤1 wk) to test our hypothesis. This information will help to quantify the time saved by BFR-assisted musculoskeletal rehabilitation. This is of particular importance for patients, because the potentially accelerated recovery of physical functioning would allow to return to their work and/or social life earlier. Furthermore, other stakeholders in the healthcare system (eg, physicians, nurses, physiotherapists, insurance companies) might benefit from that with regard to work and financial burden.
Objectives
The aim of this investigation was to determine if acute or repeated applications of ischemic preconditioning (IPC) could enhance the recovery process, following exercise induced muscle damage (EIMD).
Design
Randomized control trial.
Methods
Twenty-three healthy males were familiarised with the muscle damaging protocol (five sets of 20 drop jumps from a 0.6 m box) and randomly allocated to one of three groups: SHAM (3 x 5 min at 20 mmHg), Acute IPC (3 x 5 min at 220 mmHg) and Repeated IPC (3 days x 3 x 5 min at 220 mmHg). The indices of muscle damage measured included creatine kinase concentration ([CK]), thigh swelling, delayed onset muscle soreness, counter movement jumps (CMJ) and maximal voluntary isometric contraction (MVIC).
Results
Both acute and repeated IPC improved recovery in MVIC versus SHAM. Repeated IPC led to a faster MVIC recovery at 48 h (101.5%) relative to acute IPC (92.6%) and SHAM (84.4%) (P < 0.05). Less swelling was found for both acute and repeated IPC vs. SHAM (P < 0.05) but no group effects were found for CMJ, soreness or [CK] responses (P > 0.05).
Conclusion
Taken together, repeated IPC can enhance recovery time of MVIC more than an acute application, and both reduce swelling following EIMD, relative to a SHAM condition.
Background:
ACL reconstruction often results in an extended period of muscle atrophy and weakness. Blood flow restriction (BFR) training is a technique that has been shown to decrease muscle atrophy in a variety of populations.
Purpose:
The purpose of this systematic review was to analyze the research presented on the effect of blood flow restriction training on quadriceps muscle atrophy and circumference post ACL reconstruction.
Study design:
Systematic Review.
Methods:
Articles were reviewed using the databases Google Scholar, PubMed, and EBSCO. Keywords included blood flow restriction training, ACL reconstruction, and quadriceps.
Inclusion criteria included:
English language, peer-reviewed journals; randomized control trials; and articles including blood flow restriction and measurement of quadriceps atrophy and circumference post ACL reconstruction. Exclusion criteria included non-English language publications; studies without a control group; and articles without sufficient data to evaluate the methodology. Four studies met the selection criteria and were assessed using the GRADE scale, which analyzes the strength of a study based on study limitations, precision, consistency, directness, and publication bias. After a GRADE designation was assigned, the following information was extracted from and compared across the studies: participant demographics, cuff used, graft used during ACL reconstruction, tool used to assess muscle atrophy, protocol used, and conclusions.
Results:
Three out of four studies showed some amount of an increase in femoral muscle cross sectional area after the use of BFR combined with low-intensity resistance training (LIRT). The strength of all four studies was moderate when assessed using the GRADE scale.
Conclusion:
This review of the available evidence yields promising results regarding the use of BFR and LIRT in the remediation of femoral muscle atrophy after an ACL reconstruction. Further research is necessary before BFR can be recommended for use in clinical settings.
Level of evidence:
3a.
Background
Blood flow restriction (BFR) is a novel technique involving the use of a cuff/tourniquet system positioned around the proximal end of an extremity to maintain arterial flow while restricting venous return.
Purpose
To analyze the available literature regarding the use of BFR to supplement traditional resistance training in healthy athletes.
Study Design
Systematic review.
Methods
A systematic review was performed in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. From November to December 2018, studies that examined the effects of BFR training in athletes were identified using PubMed and OVID Medline. Reference lists from selected articles were analyzed for additional studies. The inclusion criteria for full article review were randomized studies with control groups that implemented BFR training into athletes’ resistance training workouts. Case reports and review studies were excluded. The following data were extracted: patient demographics, study design, training protocol, occlusive cuff location/pressure, maximum strength improvements, muscle size measurements, markers of sports performance (eg, sprint time, agility tests, and jump measurements), and other study-specific markers (eg, electromyography, muscular torque, and muscular endurance).
Results
The initial search identified 237 articles. After removal of duplicates and screening of titles, abstracts, and full articles, 10 studies were identified that met the inclusion criteria. Seven of 9 (78%) studies found a significant increase in strength associated with use of BFR training as compared with control; 4 of 8 (50%) noted significant increases in muscle size associated with BFR training; and 3 of 4 (75%) reported significant improvements in sport-specific measurements in the groups that used BFR training. Occlusive cuff pressure varied across studies, from 110 to 240 mm HG.
Conclusion
The literature appears to support that BFR can lead to improvements in strength, muscle size, and markers of sports performance in healthy athletes. Combining traditional resistance training with BFR may allow athletes to maximize athletic performance and remain in good health. Additional studies should be conducted to find an optimal occlusive pressure to maximize training improvements.
Registration
CRD42019118025 (PROSPERO).
An increasingly popular method for post-operative rehabilitation of an ACL reconstruction, as a substitute for traditional therapy, is blood flow restriction therapy (BFR). BFR therapy utilizes a pneumatic cuff to simulate strenuous exercise in an effort to stimulate muscle recruitment, mitigate atrophy, and promote hypertrophy in patients with load-bearing limitations. Because this is a relatively new form of therapy, there is a lack of established literature and protocol that is preventing widespread use of the therapy. This article will seek to confirm the value and validity of the utilization of BFR therapy. In order to validate the utilization of BFR, an evaluation of the science underlying BFR will be discussed as well as the technique and exercises preformed during therapy. Furthermore, analysis of other BFR literature will be utilized to lend further credence to the obtained conclusions. Based on the literature, BFR therapy mitigates atrophy through type II muscle recruitment while also stimulating hypertrophy in patients, supporting its use post-operatively. Moreover, positive results from BFR case series also lend credence to its value as a substitute for traditional therapy in patients who have weight-bearing limitations, specifically those who are recovering from anterior cruciate ligament reconstructions.
Context:
Distinct from the muscle atrophy that develops from inactivity or disuse, atrophy that occurs after traumatic joint injury continues despite the patient being actively engaged in exercise. Recognizing the multitude of factors and cascade of events that are present and negatively influence the regulation of muscle mass after traumatic joint injury will likely enable clinicians to design more effective treatment strategies. To provide sports medicine practitioners with the best strategies to optimize muscle mass, the purpose of this clinical review is to discuss the predominant mechanisms that control muscle atrophy for disuse and posttraumatic scenarios, and to highlight how they differ.
Evidence acquisition:
Articles that reported on disuse atrophy and muscle atrophy after traumatic joint injury were collected from peer-reviewed sources available on PubMed (2000 through December 2019). Search terms included the following: disuse muscle atrophy OR disuse muscle mass OR anterior cruciate ligament OR ACL AND mechanism OR muscle loss OR atrophy OR neurological disruption OR rehabilitation OR exercise.
Study design:
Clinical review.
Level of evidence:
Level 5.
Results:
We highlight that (1) muscle atrophy after traumatic joint injury is due to a broad range of atrophy-inducing factors that are resistant to standard resistance exercises and need to be effectively targeted with treatments and (2) neurological disruptions after traumatic joint injury uncouple the nervous system from muscle tissue, contributing to a more complex manifestation of muscle loss as well as degraded tissue quality.
Conclusion:
Atrophy occurring after traumatic joint injury is distinctly different from the muscle atrophy that develops from disuse and is likely due to the broad range of atrophy-inducing factors that are present after injury. Clinicians must challenge the standard prescriptive approach to combating muscle atrophy from simply prescribing physical activity to targeting the neurophysiological origins of muscle atrophy after traumatic joint injury.
Objectives:
The present randomized controlled intervention study examined the effects of practical blood flow restriction (pBFR) on maximal oxygen uptake (V̇O2max) during low intensity rowing.
Design:
Thirty-one elite rowers were either assigned to the intervention (INT) or control (CON) group, using the minimization method (Strata: Gender, Age, Height, V̇O2max).
Method:
While INT (n=16; 4 female, 12 male, 21.9±3.2 years, 180.4±8.7cm, 73.6±10.9kg, V̇O2max: 63.0±7.9ml/min/kg) used pBFR during boat- and indoor-rowing training, CON (n=15, 4 female, 11 male, 21.7±3.7 years, 180.7±8.1cm, 72.5±12.1kg, V̇O2max: 63.2±8.5ml/min/kg) completed the identical training without pBFR. pBFR of the lower limb was applied via customized elastic wraps. Training took place three times a week over 5 weeks (accumulated net pBFR: 60min/week; occlusion per session: 2-times 10min/session) and was used exclusively at low intensities (<2mmol/L). A spiroergometric ramp test (V̇O2max; 30-40W/min increase) on rowing-ergometer and one-repetition maximum test of the squat exercise (SQ1RM) was employed to assess endurance and strength capacity.
Results:
Significant group×time interactions (ηp²=0.26) in favor of INT were found for V̇O2max (+9.1±6.2%, Effect Size=1.3) compared to CON (+2.5±6.1%, ES=0.3). SQ1RM (ηp²=0.01) was not affected by the pBFR intervention.
Conclusions:
This study revealed that 15 sessions of pBFR application with a cumulative total pBFR load of 5h over a 5 weeks macrocycle remarkably increased V̇O2max. Thus, pBFR might serve as a promising means to improve aerobic capacity in highly trained elite rowers.
Background:
Despite best practice, quadriceps strength deficits often persist for years after anterior cruciate ligament reconstruction. Blood flow restriction training (BFRT) is a possible new intervention that applies a pressurized cuff to the proximal thigh that partially occludes blood flow as the patient exercises, which enables patients to train at reduced loads. This training is believed to result in the same benefits as if the patients were training under high loads.
Objective:
The objective is to evaluate the effect of BFRT on quadriceps strength and knee biomechanics and to identify the potential mechanism(s) of action of BFRT at the cellular and morphological levels of the quadriceps.
Design:
This will be a randomized, double-blind, placebo-controlled clinical trial.
Setting:
The study will take place at the University of Kentucky and University of Texas Medical Branch.
Participants:
Sixty participants between the ages of 15 to 40 years with an ACL tear will be included.
Intervention:
Participants will be randomly assigned to (1) physical therapy plus active BFRT (BFRT group) or (2) physical therapy plus placebo BFRT (standard of care group). Presurgical BFRT will involve sessions 3 times per week for 4 weeks, and postsurgical BFRT will involve sessions 3 times per week for 4 to 5 months.
Measurements:
The primary outcome measure was quadriceps strength (peak quadriceps torque, rate of torque development). Secondary outcome measures included knee biomechanics (knee extensor moment, knee flexion excursion, knee flexion angle), quadriceps muscle morphology (physiological cross-sectional area, fibrosis), and quadriceps muscle physiology (muscle fiber type, muscle fiber size, muscle pennation angle, satellite cell proliferation, fibrogenic/adipogenic progenitor cells, extracellular matrix composition).
Limitations:
Therapists will not be blinded.
Conclusions:
The results of this study may contribute to an improved targeted treatment for the protracted quadriceps strength loss associated with anterior cruciate ligament injury and reconstruction.
Objective:
To describe the successful rehabilitation of a distal biceps brachii tendon reattachment following an acute traumatic tendon rupture.
Clinical features:
A 30-year-old weightlifter presented five days post-op after a left distal biceps tendon repair. A three month one pound weight-restriction was recommended by the attending surgeon. Active and passive elbow and wrist range of motion were markedly reduced with profuse post-operative swelling and bruising noted upon initial inspection.
Intervention and outcome:
An accelerated treatment program was prescribed that included soft tissue therapy, scar mobilization, laser therapy, kinesiology tape and rehabilitative exercise. A novel training method known as blood flow restriction (BFR) training was utilized throughout the rehabilitative process to maximize recovery and retain muscle mass and strength. The weightlifter returned to near pre-injury activity level after 3.5 months. Treatment, exercise and BFR protocols are provided.
New approaches that promise more for less rarely pan out despite the hopes of physical therapists. In this Viewpoint, the author discusses blood flow restriction training, an intervention claiming that some low-intensity exercise performed while wearing a blood pressure cuff will result in strength gains, improved performance, shorter postexercise recovery, and pain reduction. J Orthop Sports Phys Ther 2019;49(5):294-298. doi:10.2519/jospt.2019.0608.
Background::
Blood flow restriction (BFR) training involves low-weight exercises performed under vascular occlusion via an inflatable cuff. For patients who cannot tolerate high-load exercises, BFR training reportedly provides the benefits of high-load regimens, with the advantage of less tissue and joint stress.
Hypothesis::
Low-load BFR training is safe and efficacious for strengthening muscle groups proximal, distal, and contralateral to tourniquet placement in the lower extremities.
Study design::
Randomized controlled trial.
Level of evidence::
Level 1.
Methods::
This was a randomized controlled trial of healthy participants completing a standardized 6-week course of BFR training. Patients were randomized to BFR training on 1 extremity or to a control group. Patients were excluded for cardiac, pulmonary, or hematologic disease; pregnancy; or previous surgery in the extremity. Data collected at baseline and completion included limb circumferences and strength testing.
Results::
The protocol was completed by 26 patients, providing 16 BFR and 10 control patients (mean patient age, 27 years; 62% female). A statistically greater increase in strength was seen proximal and distal to the BFR tourniquet when compared with both the nontourniquet extremity and the control group ( P < 0.05). Approximately twice the improvement was seen in the BFR group compared with controls. Isokinetic testing showed greater increases in knee extension peak torque (3% vs 11%), total work (6% vs 15%), and average power (4% vs 12%) for the BFR group ( P < 0.04). Limb circumference significantly increased in both the thigh (0.8% vs 3.5%) and the leg (0.4% vs 2.8%) compared with the control group ( P < 0.01). Additionally, a significant increase occurred in thigh girth (0.8% vs 2.3%) and knee extension strength (3% vs 8%) in the nontourniquet BFR extremity compared with the control group ( P < 0.05). There were no reported adverse events.
Conclusion::
Low-load BFR training led to a greater increase in muscle strength and limb circumference. BFR training had similar strengthening effects on both proximal and distal muscle groups. Gains in the contralateral extremity may corroborate a systemic or crossover effect.
Clinical relevance::
BFR training strengthens muscle groups proximal, distal, and contralateral to cuff placement. Patients undergoing therapy for various orthopaedic conditions may benefit from low-load BFR training with the advantage of less tissue stress.
Abstract: Blood flow restriction (BFR) training involves occluding venous outflow while maintaining arterial inflow by the application of an extremity tourniquet after surgery. BFR ultimately reduces oxygen delivery to muscle cells, similar to an anaerobic environment, and allows patients to exercise with low resistance and stimulates muscle hypertrophy and strength using heavy resistance. Thus orthopaedic surgeons and physical therapists are incorporating this type of training into their postoperative rehabilitation protocols, particularly after injuries or surgical procedures about the knee joint. The purpose of this Technical Note is to describe a BFR clinical application technique and to report on the indications, safety considerations, and postoperative knee surgery rehabilitation protocols for BFR.