Blood Flow Restriction Resistance Exercise Research Articles

Non‐failure blood flow restricted exercise induces similar muscle adaptations and less discomfort than failure protocols

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, BFRE to failure 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 exercise 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 exercise 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 enables 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.

Skeletal Muscle Mitochondrial Protein Synthesis and Respiration Increase With Low-Load Blood Flow Restricted as Well as High-Load Resistance Training.

Purpose: It is well established that high-load resistance exercise (HLRE) can stimulate myofibrillar accretion. Additionally, recent studies suggest that HLRE can also stimulate mitochondrial biogenesis and respiratory function. However, in several clinical situations, the use of resistance exercise with high loading may not constitute a viable approach. Low-load blood flow restricted resistance exercise (BFRRE) has emerged as a time-effective low-load alternative to stimulate myofibrillar accretion. It is unknown if BFRRE can also stimulate mitochondrial biogenesis and respiratory function. If so, BFRRE could provide a feasible strategy to stimulate muscle metabolic health.Methods: To study this, 34 healthy previously untrained individuals (24 ± 3 years) participated in BFRRE, HLRE, or non-exercise control intervention (CON) 3 times per week for 6 weeks. Skeletal muscle biopsies were collected; (1) before and after the 6-week intervention period to assess mitochondrial biogenesis and respiratory function and; (2) during recovery from single-bout exercise to assess myocellular signaling events involved in transcriptional regulation of mitochondrial biogenesis. During the 6-week intervention period, deuterium oxide (D2O) was continuously administered to the participants to label newly synthesized skeletal muscle mitochondrial proteins. Mitochondrial respiratory function was assessed in permeabilized muscle fibers with high-resolution respirometry. Mitochondrial content was assessed with a citrate synthase activity assay. Myocellular signaling was assessed with immunoblotting.Results: Mitochondrial protein synthesis rate was higher with BFRRE (1.19%/day) and HLRE (1.15%/day) compared to CON (0.92%/day) (P < 0.05) but similar between exercise groups. Mitochondrial respiratory function increased to similar degree with both exercise regimens and did not change with CON. For instance, coupled respiration supported by convergent electron flow from complex I and II increased 38% with BFRRE and 24% with HLRE (P < 0.01). Training did not alter citrate synthase activity compared to CON. BFRRE and HLRE elicited similar myocellular signaling responses.Conclusion: These results support recent findings that resistance exercise can stimulate mitochondrial biogenesis and respiratory function to support healthy skeletal muscle and whole-body metabolism. Intriquingly, BFRRE produces similar mitochondrial adaptations at a markedly lower load, which entail great clinical perspective for populations in whom exercise with high loading is untenable.

Delayed myonuclear addition, myofiber hypertrophy, and increases in strength with high-frequency low-load blood flow restricted training to volitional failure.

The purpose of the present study was to investigate muscle hypertrophy, strength, and myonuclear and satellite cell (SC) responses to high-frequency blood flow-restricted resistance exercise (BFRRE). Thirteen individuals [24 ± 2 yr (mean ± SD), 9 men] 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 one repetition maximum (1RM) were conducted with partial blood flow restriction (90-100 mmHg). Muscle samples obtained before, during, 3 days, 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. With the first block of BFRRE, SC number increased in both fiber types (70%-80%, P < 0.05), whereas 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%, whereas the number of SCs (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, whereas myostatin, IGF1R, MyoD, myogenin, cyclinD1 and -D2 mRNA did not change until 3-10 days postintervention. 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. NEW & NOTEWORTHY In line with previous studies, we demonstrate that high-frequency low-load blood flow-restricted resistance exercise (HF-BFRRE) can elicit robust increases in satellite cell and myonuclei numbers, along with gains in muscle size and strength. However, our results also suggest that these processes can be delayed and that with very strenuous HF-BFRRE, there may even be transient muscle fiber atrophy, presumably because of accumulated stress responses. Our findings have implications for the prescription of BFR exercise.

The systemic myokine response of decorin, interleukin-6 (IL-6) and interleukin-15 (IL-15) to an acute bout of blood flow restricted exercise.

Blood flow restricted resistance exercise (BFR-RE) is an emerging hypertrophy training modality. A complete profile of its mechanisms of action has yet to be elucidated. Cytokines are universal intercellular messengers. Recent research has implicated certain cytokines (termed "myokines") in skeletal muscle hypertrophy pathways; however, little research has been conducted on the systemic myokine response to BFR-RE as potential hypertrophic biomarkers. Therefore, this project was conducted to determine any differences in the systemic myokine response between BFR-RE and control conditions. The appearance of systemic myokines interleukin-6 (IL-6), interleukin-15 (IL-15), and decorin were measured following acute bouts of low-load resistance exercise, BFR-RE, and high-load resistance exercise in physically active young males to determine if BFR-RE modifies the exercise-induced systemic myokine response. No measurable levels of IL-6 were observed during the project. No significant effects were observed for IL-15. A significant time (11.91% increase pre to post exercise; p < 0.05) but no condition or condition by time effect was observed for decorin. These findings suggest that BFR-RE does not modify the systemic myokine appearance of IL-6, IL-15, or decorin when compared to control conditions.

Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk.

Synopsis Restoration of skeletal muscle mass and strength is critical to successful outcomes following orthopaedic surgery. Blood flow restriction (BFR) resistance exercise has emerged as a promising means of augmenting traditional low-intensity physical rehabilitation exercise and has yielded successful outcomes in a wide range of applications. Though BFR is well tolerated and safe for most individuals, patients who have undergone orthopaedic surgery may be an exception, due to their heightened risk for venous thromboembolism (VTE). While the pathogenesis of VTE is multifactorial and specific to the individual, it is commonly described as a combination of blood stasis, endothelial injury, and alterations in the constituents of the blood leading to hypercoagulability. The collective literature suggests that, given the pathogenic mechanisms of VTE, limited use of a wide, partially occluding cuff during resistance exercise should be low risk, and the likelihood that BFR would directly cause a VTE event is remote. Alternatively, it is plausible that BFR may enhance blood flow and promote fibrinolysis. Of greater concern is the individual with pre-existing asymptomatic VTE, which could be dislodged during BFR. However, it is unknown whether the direct risk associated with BFR is greater than the risk accompanying traditional exercise alone. Presently, there are no universally agreed-upon standards indicating which postsurgical orthopaedic patients may perform BFR safely. While excluding all these patients from BFR may be overly cautious, clinicians need to thoroughly screen for VTE signs and symptoms, be cognizant of each patient's risk factors, and use proper equipment and prescription methods prior to initiating BFR. J Orthop Sports Phys Ther 2019;49(1):17-27. Epub 12 Sep 2018. doi:10.2519/jospt.2019.8375.

Comparison of the acute perceptual and blood pressure response to heavy load and light load blood flow restriction resistance exercise in anterior cruciate ligament reconstruction patients and non-injured populations

ObjectivesTo compare the acute perceptual and blood pressure responses to: 1) light load blood flow restriction resistance exercise (BFR-RE) in non-injured individuals and anterior cruciate ligament reconstruction (ACLR) patients; and 2) light load BFR-RE and heavy load RE (HL-RE) in ACLR patients. DesignBetween-subjects, partially-randomised. MethodsThis study comprised 3 groups: non-injured BFR-RE (NI-BFR); ACLR patients BFR-RE (ACLR-BFR); ACLR patients HL-RE (ACLR-HL). NI-BFR and ACLR-BFR performed 4 sets (30, 15, 15, 15 reps, total = 75 reps, 30s inter-set rest) of unilateral leg press exercise at 30% 1RM with continuous BFR at 80% limb occlusive pressure. ACLR-HL performed 3 × 10 reps (Total = 30 reps, 30s inter-set rest) of unilateral leg press exercise at 70% 1RM. Perceived exertion (RPE), muscle pain, knee pain and pre- and 5-min post-exercise blood pressure were measured. ResultsRPE was higher in ACLR-BFR compared to NI-BFR (p < 0.05). Muscle pain was higher in NI-BFR and ACLR-BFR compared to ACLR-HL (p < 0.05). Knee pain was lower in ACLR-BFR compared to ACLR-HL (p < 0.01). There were no differences in blood pressure. ConclusionThese responses to BFR exercise may not limit application and favourably influence knee pain throughout ACLR rehabilitation training programmes. These findings can help inform practitioners' decisions to utilise this tool.

Mood Effects of Blood Flow Restriction Resistance Exercise Among Basketball Players.

This study compared the acute effects of resistance exercise with and without blood flow restriction (BFR) on basketball players' mood states. A total of 11 male basketball players (M age = 19.9, SD = 2.8 years; M height = 180.8, SD = 7.8 cm; M weight = 71.1, SD = 9.1 kg; M body mass index = 22.1, SD = 1.9 kg/m2) were randomly assigned to two experimental conditions: (a) low-load resistance exercise with BFR (LLRE + BFR) and high-load resistance exercise (HLRE) without BFR. We measured mood state with the Brunel Mood Scale before and after each session. There was a significant interaction effect such that there was increased fatigue over time with LLRE + BFR ( p = .001, Δ% = 169.2). Regarding total mood disorder, there were significant pre and postexercise differences between athletes exposed to both the LLRE + BFR and HLRE conditions ( p = .048) and a decharacterization of the iceberg mood profile in the post-training LLRE + BFR condition. LLRE + BFR, compared to HLRE, promoted an acute negative effect on mood state, decharacterization of the iceberg profile, total mood disturbance, and increased participant fatigue, suggesting that this method of strength training should be avoided before sports competitions.

Delayed Onset Muscle Soreness and Perceived Exertion After Blood Flow Restriction Exercise.

Brandner, CR, and Warmington, SA. Delayed onset muscle soreness and perceived exertion after blood flow restriction exercise. J Strength Cond Res 31(11): 3101-3108, 2017-The purpose of this study was to determine the perceptual responses to resistance exercise with heavy loads (80% 1 repetition maximum [1RM]), light loads (20% 1RM), or light loads in combination with blood flow restriction (BFR). Despite the use of light loads, it has been suggested that the adoption of BFR resistance exercise may be limited because of increases in delayed onset muscle soreness (DOMS) and perceived exertion. Seventeen healthy untrained males participated in this balanced, randomized cross-over study. After 4 sets of elbow-flexion exercise, participants reported ratings of perceived exertion (RPE), with DOMS also recorded for 7 days after each trial. Delayed onset muscle soreness was significantly greater for low-pressure continuous BFR (until 48 hours postexercise) and high-pressure intermittent BFR (until 72 hours postexercise) than for traditional heavy-load resistance exercise and light-load resistance exercise. In addition, RPE was higher for heavy-load resistance exercise and high-pressure intermittent BFR than for low-pressure continuous BFR, with all trials greater than light-load resistance exercise. For practitioners working with untrained participants, this study provides evidence to suggest that to minimize the perception of effort and postexercise muscle soreness associated with BFR resistance exercise, continuous low-pressure application may be more preferential than intermittent high-pressure application. Importantly, these perceptual responses are relatively short-lived (∼2 days) and have previously been shown to subside after a few exercise sessions. Combined with smaller initial training volumes (set × repetitions), this may limit RPE and DOMS to strengthen uptake and adherence and assist in program progression for muscle hypertrophy and gains in strength.

Cyclical blood flow restriction resistance exercise: a potential parallel to remote ischemic preconditioning?

Remote ischemic preconditioning (RIPC) is characterized by the cyclical application of limb blood flow restriction and reperfusion and has been shown to protect vital organs during a subsequent ischemic insult. Blood flow restriction exercise (BFRE) similarly combines bouts of blood flow restriction with low-intensity exercise and thus could potentially emulate the protection demonstrated by RIPC. One concern with BFRE, however, is the potential for an augmented rise in sympathetic outflow due to greater activation of the exercise pressor reflex. Because of the use of lower workloads, however, we hypothesized that BFRE would elicit an attenuated increase in sympathetic outflow [assessed via plasma norepinephrine (NE) and mean arterial pressure (MAP)] and middle cerebral artery velocity (MCAv) when compared with conventional exercise (CE). Fifteen subjects underwent two leg press exercise interventions: 1) BFRE-220 mmHg bilateral thigh occlusion at 20% 1 rep-max (1RM), and 2) CE-65% 1RM without occlusion. Each condition consisted of 4 × 5-min cycles of exercise, with 3 × 10-reps in each cycle. Five minutes of rest and reperfusion (for BFRE) followed each cycle. MAP increased with exercise (P < 0.001) and was 4-5 mmHg higher with CE versus BFRE (P ≤ 0.09). Mean MCAv also increased with exercise (P < 0.001) and was higher with CE compared with BFRE during the first bout of exercise only (P = 0.07). Plasma NE concentration increased with CE only (P < 0.001) and was higher than BFRE throughout exercise (P ≤ 0.02). The attenuated sympathetic response, combined with similar cerebrovascular responses, suggest that cyclical BFRE could be explored as an alternative to CE in the clinical setting.

Acute Effects of Blood Flow Restriction Resistance Exercise in a Head-down Tilt Position on Growth Hormone and Insulin-like Growth Factor-I Release

Muscular atrophy is common among astronauts while in spaceflight. Growth Hormone (GH) and IGF-I are key hormones with regards to the preservation and growth of skeletal muscle tissue. Low intensity blood flow restriction (BFR) resistance exercise is a newer training modality employed to various populations to enhance muscle growth, yet has not been thoroughly explored in the astronaut population. PURPOSE: To determine the effects of low intensity BFR in a head-down tilt position on the acute release of GH and IGF-I. METHODS: Twelve college-aged males with resistance exercise experience were included in the study. The first of three sessions consisted of informed consent, demographic measurements, and 3RM testing. The two experimental sessions consisted of subjects resting in a -6 deg head-down tilt position for 2 hr. Upon rest completion, while tilted, subjects performed the exercise protocol at 30% of estimated 1RM for the following exercises: close-grip bench press, dumbbell bicep curls, and dumbbell triceps extensions. Exercises were performed with or without BFR (160 mmHg) to the upper arms in a counterbalanced order. Venus blood draws (15 mL) occurred 10 min prior to tilt, 10-15 min post exercise protocol, and 24 hr post exercise protocol and were assayed in duplicate. Two 2 x 2 Factorial ANOVAs with repeated measures were utilized for statistical analysis of the dependent variables (GH, IGF-I). Alpha levels were set at p < 0.05. RESULTS: A significant interaction was found between exercise condition and time for GH (p < .05). No significant interaction was found between exercise condition and time for IGF-I (p > .05). No significant mean difference was observed between BFR and no BFR for IGF-I (p >.05). A significant mean difference was observed pre to post exercise protocol for IGF-I (p < .05). CONCLUSION: A low intensity BFR exercise protocol in a head-down tilt position elicited a large increase in systemic GH concentrations from pre to post exercise. Post exercise GH levels were elevated to a much greater extent with BFR compared to no BFR. A low intensity BFR modality may be beneficial to employ to astronauts while in spaceflight or post spaceflight to help promote muscular tissue growth.

Abstract WP157: Sympathetic and Cerebrovascular Responses to Blood Flow Restriction Resistance Exercise: A Potential Parallel to Remote Ischemic Preconditioning?

Introduction: Remote ischemic preconditioning (RIPC) is characterized by the cyclic application of limb blood flow restriction and reperfusion, and has been shown to protect the brain during a subsequent ischemic insult. Blood flow restriction exercise (BFRE) is a novel training modality that similarly combines bouts of blood flow restriction and reperfusion with low-intensity exercise and thus could potentially emulate the protection demonstrated by RIPC. One concern with clinical application of BFRE is the potential for an augmented exercise pressor reflex, resulting in an unsafe rise in sympathetic outflow. Due to the use of lower workloads, however, we hypothesized that BFRE would exhibit an attenuated increase in sympathetic outflow, mean arterial pressure (MAP), and brain blood flow. Methods: 11 subjects (6M/5F; age 28±2 yrs) underwent 2 leg press exercise interventions separated by ≥1 month: 1. BFRE - 220 mmHg thigh occlusion during 4 cycles x 5-min of exercise, consisting of 3 x 10 reps at 20% of 1 rep-max (1RM), and; 2. Conventional exercise (CE) - 4 cycles x 5-min of exercise, consisting of 3 x 10 reps at 65% 1RM without occlusion. 5-min of rest and reperfusion (for BFRE) followed each cycle. MAP, mean middle cerebral artery velocity (MCAv), cerebral oxygen saturation (ScO 2 ), and plasma norepinephrine concentrations ([NE]) were compared between trials. Results: MAP increased with exercise under both conditions (P&lt;0.001) and was higher (P≤0.03) with CE vs. BFRE for each cycle (1. 107±3 vs. 103±2 mmHg, 2. 107±2 vs. 103±2 mmHg, 3. 107±2 vs. 103±2 mmHg, 4. 107±2 vs. 104±2 mmHg). MCAv and ScO 2 (N=10) increased over time (P&lt;0.001) with no difference between conditions for MCAv (P=0.83), while ScO 2 was higher for CE vs. BFRE (65±1 vs. 62±1%, P=0.05). Plasma [NE] (N=7) increased over time for both conditions (P=0.08) and was higher for CE vs. BFRE (757±103 vs. 524±71 pg/ml, P=0.09). Conclusions: BFRE elicited an attenuated sympathetic response compared to CE as evidenced by lower MAP and plasma [NE]. The lower ScO 2 (i.e., increased oxygen extraction) and no difference in MCAv responses suggests greater cerebral metabolic demand with BFRE. These findings indicate that BFRE could be explored as an alternative to CE in the clinical setting such as stroke-rehabilitation.

Hemodynamic Responses to Blood Flow Restriction and Resistance Exercise to Muscular Failure.

The aim of the present study was to compare hemodynamic responses between blood flow-restricted resistance exercise (BFR-RE), high-intensity resistance exercise (HI-RE) and low-intensity resistance exercise (LI-RE) performed to muscular failure. 12 men (age: 20±3 years; body mass: 73.5±9 kg; height: 174±6 cm) performed 4 sets of leg press exercises using BFR-RE (30% of 1-RM), HI-RE (80% of 1-RM) and LI-RE (30% of 1-RM) protocols. Systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV), cardiac output (CO) and total peripheral vascular resistance (TPR) were measured on a beat-to-beat continuous basis by a noninvasive photoplethysmographic arterial pressure device. The HI-RE and LI-RE showed higher values (P<0.05) in all of the sets than the BFR-RE for SBP, DBP, HR. Additionally, HI-RE showed higher SBP (4th set) and DBP (all sets) (P<0.05) values than the LI-RE. However, the SV, CO and TPR showed significantly greater values for LI-RE compared to HI-RE and BFR-RE (P<0.05). In conclusion, the results of this study indicate that the BFR-RE promotes a lower hemodynamic response compared to the HI-RE and LI-RE performed to muscular failure.

Blood Flow Restricted Exercise Compared to High Load Resistance Exercise During Unloading.

Bed rest studies have shown that high load (HL) resistance training can mitigate the loss of muscle size and strength during musculoskeletal unloading; however, not all individuals are able to perform HL resistance exercise. Blood flow restricted (BFR) resistance exercise may be a novel way to prevent maladaptation to unloading without requiring HL exercise equipment. This study evaluated the muscular training adaptations to HL and BFR resistance training during unilateral lower limb suspension (ULLS), a human limb unloading model. ULLS allows for evaluation of exercise training in both weight-bearing and nonweight-bearing legs within the same individual. There were 13 participants who completed 25 d of ULLS and were counterbalanced to: 1) HL, N = 6; or 2) BFR, N = 7, training groups. During ULLS, HL and BFR performed unilateral leg press and heel raise exercise (3 d/wk). In weight-bearing legs, both HL and BFR increased knee extensor muscle cross-sectional area (CSA) and strength. In nonweight-bearing legs, knee extensor CSA and strength increased only in HL and decreased with BFR. HL and BFR resistance exercise were both effective exercise programs for the weight-bearing leg. However, BFR exercise was not as effective as HL resistance exercise in the nonweight-bearing leg. These data show that exercise that improved muscle CSA and strength in ambulatory weight-bearing conditions was not sufficient to maintain muscle function during unloading. For the preservation of muscle CSA and strength, BFR exercise should be considered an adjunct but not a primary exercise countermeasure for future space missions. Hackney KJ, Downs ME, Ploutz-Snyder L. Blood flow restricted exercise compared to high load resistance exercise during unloading. Aerosp Med Hum Perform. 2016; 87(8):688-696.

Muscle damage and repeated bout effect following blood flow restricted exercise.

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). Seventeen healthy young men were allocated into two groups completing two exercise bouts separated by 14days. 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. 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. 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.

Corticomotor Excitability is Increased Following an Acute Bout of Blood Flow Restriction Resistance Exercise.

We used transcranial magnetic stimulation (TMS) to investigate whether an acute bout of resistance exercise with blood flow restriction (BFR) stimulated changes in corticomotor excitability (motor evoked potential, MEP) and short-interval intracortical inhibition (SICI), and compared the responses to two traditional resistance exercise methods. Ten males completed four unilateral elbow flexion exercise trials in a balanced, randomized crossover design: (1) heavy-load (HL: 80% one-repetition maximum [1-RM]); (2) light-load (LL; 20% 1-RM) and two other light-load trials with BFR applied; (3) continuously at 80% resting systolic blood pressure (BFR-C); or (4) intermittently at 130% resting systolic blood pressure (BFR-I). MEP amplitude and SICI were measured using TMS at baseline, and at four time-points over a 60 min post-exercise period. MEP amplitude increased rapidly (within 5 min post-exercise) for BFR-C and remained elevated for 60 min post-exercise compared with all other trials. MEP amplitudes increased for up to 20 and 40 min for LL and BFR-I, respectively. These findings provide evidence that BFR resistance exercise can modulate corticomotor excitability, possibly due to altered sensory feedback via group III and IV afferents. This response may be an acute indication of neuromuscular adaptations that underpin changes in muscle strength following a BFR resistance training programme.

The efficacy of blood flow restricted exercise: A systematic review & meta-analysis.

To systematically search and assess studies that have combined blood flow restriction (BFR) with exercise, and to perform meta-analysis of the reported results to quantify the effectiveness of BFR exercise on muscle strength and hypertrophy. A systematic review. A computer assisted database search was conducted for articles investigating the effect of exercise combined with BFR on muscle hypertrophy and strength. A total of 916 hits were screened in order based on title, abstract, and full article, resulting in 47 articles that fit the review criteria. A total of 400 participants were included from 19 different studies measuring muscle strength increases when exercise is combined with BFR. Exercise was separated into aerobic and resistance exercise. Resulting from BFR aerobic exercise, there was a mean strength improvement of 0.4Nm between the experimental group and control group, while BFR resistance exercise resulted in a mean improvement of 0.3kg. A total of 377 participants were included in 19 studies measuring muscle size increase (cross sectional area) when exercise was combined with BFR. The mean difference in muscle size between the experimental group and control group was 0.4cm(2). Current evidence suggests that the addition of BFR to dynamic exercise training is effective for augmenting changes in both muscle strength and size. This effect was consistent for both resistance training and aerobically-based exercise, although the effect sizes varied. The magnitude of observed changes are noteworthy, particularly considering the relatively short duration of the average intervention.

Blood flow restricted exercise for athletes: A review of available evidence.

This study aimed to collate current evidence regarding the efficacy of various blood flow restriction (BFR) strategies for well-trained athletes, and to provide insight regarding how such strategies can be used by these populations. Review article. Studies that had investigated the acute or adaptive responses to BFR interventions in athletic participants were identified from searches in MEDLINE (PubMed), SPORTDiscus (EBSCO) and Google Scholar databases up to April 2015. The reference lists of identified papers were also examined for relevant studies. Twelve papers were identified from 11 separate investigations that had assessed acute and adaptive responses to BFR in athletic cohorts. Of these, 7 papers observed enhanced hypertrophic and/or strength responses and 2 reported alterations in the acute responses to low-load resistance exercise when combined with BFR. One paper had examined the adaptive responses to moderate-load resistance training with BFR, 1 noted improved training responses to low-work rate BFR cardiovascular exercise, and 1 reported on a case of injury following BFR exercise in an athlete. Current evidence suggests that low-load resistance training with BFR can enhance muscle hypertrophy and strength in well-trained athletes, who would not normally benefit from using light loads. For healthy athletes, low-load BFR resistance training performed in conjunction with normal high-load training may provide an additional stimulus for muscular development. As low-load BFR resistance exercise does not appear to cause measureable muscle damage, supplementing normal high-load training using this novel strategy may elicit beneficial muscular responses in healthy athletes.

Blood Flow Restricted Resistance Exercise Increases Hypertrophy in National Level Powerlifters

Blood flow restricted resistance exercise (BFRE) has been shown to induce muscle mass gains in untrained subjects, elderly, patients recovering from knee surgery, and athletes. However, the effects of BFRE in highly trained strength athletes are largely unknown. PURPOSE: The aim of the present study was to investigate the effects of including two blocks of frequent BFRE during six weeks of periodized strength training on muscle growth and strength in powerlifters. METHODS: 17 national level powerlifters (25±6 years (mean±SD); 15 men, and 2 women) volunteered for the study. The powerlifters were randomized in to two groups: a BFRE group (BFR; n=9) that performed two blocks (week 1 and week 3) of five BFRE front squat sessions during the 6-week strength training period, and a control group (CON; n=8) performing normal front squats (∼70% of 1RM). The BFRE protocol consisted of four sets to voluntary failure (30 s rest between sets) at 25-30% of one repetition maximum (1RM). Elastic knee bands were wrapped around the upper thighs to apply a pressure of ∼120 mmHg (verified with an underlying pressure cuff in the first session). Muscle growth was assessed as changes in thickness and cross sectional area (CSA) of m. vastus lateralis and m. rectus femoris, as well as thickness of m. vastus medialis, using ultrasound imaging. Strength was measured as 1RM in front squat and isokinetic peak torque (60 degrees per second) in leg extension. RESULTS: The BFR group showed a significantly larger increase in thickness of m. vastus lateralis (mean±SD, BFR: 4.7±3.3% vs. CON: -0.8±5.0%; p=0.02), m. rectus femoris (BFR: 5.0±2.8% vs. CON: -1.3±5.9%; p=0.01) and m. vastus medialis (BFR: 1.9±2.2% vs. CON: -2.7±4.9%; p=0.02), compared to CON group. Similarly, CSA of m. vastus lateralis increased more in the BFR group (7.7±6.5% vs. 0.5±4.3%, p=0.04). In CSA changes of m. rectus femoris, a tendency towards higher increases was observed in favor of the BFR group (BFR: 6.8±7.5% vs. CON: 1.4±3.9%; p=0.09). Changes in 1RM in front squat, as well as for isokinetic peak torque in leg extension, did not differ significantly between groups. CONCLUSION: The inclusion of ten BFR sessions produced significantly larger gains in muscle thickness and CSA than normal training during 6 weeks of strength training. However, no differences were observed in strength.

Short-Term Effects of Blood Flow Restricted Resistance Training in Older Adults at Risk of Mobility Limitations

Improvements in muscle strength in older adults have been observed following short-term (6-weeks) high-load (HL) resistance training. Blood flow restricted (BFR) resistance training using low loads has also resulted in strength gains. However, it is unknown whether HL and BFR resistance exercise produce similar effects on hypertrophy and strength gains following short duration training. PURPOSE: To compare lower extremity strength, hypertrophy and functional adaptations to 6-weeks of HL and BFR training in older adults at risk of mobility limitations. METHODS: Twenty-six older adults (76.7 ± 7.8 years; 26.2 ±3.4 kg·m-2) who possessed low knee muscle strength placing them at risk of developing mobility limitations participated in the study. They were randomly assigned to perform twice weekly sessions of HL (70% 1-RM), BFR (30% 1-RM coupled with a vascular restriction of 1.5 times systolic blood pressure at the proximal thigh) or attention control (CON) for six-weeks. HL and BFR groups engaged in three sets of leg extension (LE), leg press (LP), and leg curl resistance training to muscular failure. The CON group performed three sets of light upper body resistance and flexibility training that was not expected to result in muscle adaptations. LE and LP 1-RM, quadriceps cross-sectional area (CSA) via magnetic resonance imaging, and 400 m walking speed were assessed before and after training. RESULTS: There were clear changes in CSA and strength (group x time interaction, P<0.01) in the training groups and there were no changes in the CON group (P>0.05). HL and BFR groups demonstrated a 3% and 4% increase in CSA, respectively (P<0.05). LE 1-RM increased following HL (40%; P<0.01) and BFR (22%; P<0.01) training. LP 1-RM increased 18% and 8% in the HL and BFR groups, respectively (P<0.01). There were no differences in the CSA and strength adaptations between the HL and BFR groups (P>0.05). Walking speed did not significantly change in any group (P>0.05). CONCLUSION: Short-term HL and BFR resistance training show similar improvements in lower extremity muscle strength and CSA in older adults at risk of mobility limitations. This suggests that BFR resistance training may be a viable modality for older adults who are unable to perform HL training. Supported by NIH grant 1R15 A6040700-01A1.

A review on the mechanisms of blood-flow restriction resistance training-induced muscle hypertrophy.

It has traditionally been believed that resistance training can only induce muscle growth when the exercise intensity is greater than 65% of the 1-repetition maximum (RM). However, more recently, the use of low-intensity resistance exercise with blood-flow restriction (BFR) has challenged this theory and consistently shown that hypertrophic adaptations can be induced with much lower exercise intensities (<50% 1-RM). Despite the potent hypertrophic effects of BFR resistance training being demonstrated by numerous studies, the underlying mechanisms responsible for such effects are not well defined. Metabolic stress has been suggested to be a primary factor responsible, and this is theorised to activate numerous other mechanisms, all of which are thought to induce muscle growth via autocrine and/or paracrine actions. However, it is noteworthy that some of these mechanisms do not appear to be mediated to any great extent by metabolic stress but rather by mechanical tension (another primary factor of muscle hypertrophy). Given that the level of mechanical tension is typically low with BFR resistance exercise (<50% 1-RM), one may question the magnitude of involvement of these mechanisms aligned to the adaptations reported with BFR resistance training. However, despite the low level of mechanical tension, it is plausible that the effects induced by the primary factors (mechanical tension and metabolic stress) are, in fact, additive, which ultimately contributes to the adaptations seen with BFR resistance training. Exercise-induced mechanical tension and metabolic stress are theorised to signal a number of mechanisms for the induction of muscle growth, including increased fast-twitch fibre recruitment, mechanotransduction, muscle damage, systemic and localised hormone production, cell swelling, and the production of reactive oxygen species and its variants, including nitric oxide and heat shock proteins. However, the relative extent to which these specific mechanisms are induced by the primary factors with BFR resistance exercise, as well as their magnitude of involvement in BFR resistance training-induced muscle hypertrophy, requires further exploration.