Blood Flow Restriction Resistance Training Research Articles

Effect of Blood Flow Restricted Cycle Training on Oxygen uptake kinetics during Exercise

A number of studies have illustrated that blood flow restricted (BFR) resistance training increasing muscle function even when low-intensity training is utilized. Recently BFR has also applied to aerobic training; however less is known about the effect of aerobic training with BFR on the oxygen uptake (VO2) kinetic responses during exercise with or without BFR. PURPOSE: To elucidate the effects of 8-weeks cycle training with BFR on VO2 kinetics at the onset of constant-load cycle exercise with or without BFR. METHODS: Eighteen healthy subjects were randomly assigned to BFR (n = 9; 22±5 yrs) or no BFR group serving as the control (CON; n = 9; 21±2 yrs). Both groups trained for 30 minutes, 3 days/week for 8 weeks. BFR was performed for 5 minutes every 10 minutes by applying cuffs to the upper thighs. Breath-by-breath VO2 was measured during the performance of 5-min moderate intensity (below the lactate threshold) or 6-min heavy intensity exercise (above the lactate threshold) without BFR at Pre-, 4 weeks after (Mid-), and Post-training. At Post, we also measured VO2 kinetics during exercise with BFR (Post+BFR). Two-way repeated ANOVAs were used (BFR vs CON and Pre vs Mid vs Post vs Post+BFR) with significance accepted as p<0.05; and Tukey’s post hoc tests utilized as needed. RESULTS: Although time constant (τ) of VO2 kinetics at the fast component during moderate exercise fitted the exponential model was significantly faster in Mid and Post than that of Pre (26.8 to 16.3 and 15.5 s and 27.5 to 22.1 and 18.5 s in BFR and CON, p<0.05, respectively), significant group-by-time interaction was not detected. The amplitude of the VO2 slow component during heavy exercise significantly decreased in Mid and Post than that of Pre (281 to 103 and 128 mL/min and 300 to 154 and 160 mL/min in BFR and CON, p<0.05, respectively), while a significant group-by-time interaction was not detected. Both τ of VO2 kinetics during moderate exercise and the amplitude of the VO2 slow component during heavy exercise significantly increased from Post to Post+BFR (19.1 and 28.0 s, and 266 and 256 mL/min in BFR and CON, p<0.05, respectively); however significant group-by-time interactions were not detected either. CONCLUSION: Appling the BFR to eight-weeks cycle training showed no further change in VO2 kinetics at the onset of exercise. Supported by KAKENHI (23700788)

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 Effect of Low- Intensity Resistance Training with Blood Flow Restriction on Serum Cortisol and Testosterone Levels in Young Men

Background: Based on the research evidence, the efficiency of resistance exercises depends on the changes in the hormones level to improve the muscle strength and mass. Objectives: This study aimed to investigate the effect of a short course blood flow restricted resistance training on serum cortisol and testosterone levels in young men. Patients and Methods: A total of 30 healthy young men (aged 19 - 24 years) were volunteered for this study. Subjects were randomly assigned into three groups: low-intensity blood flow restricted (LIBFR) (n = 15) resistance exercise group (3 sets of 15 repetitions at 20% of 1RM (one repetition maximum)), traditional high-intensity without blood flow restriction (HIWBFR) (n = 12) resistance exercise group (3 sets of 10 repetitions at 80% of 1RM), and a control group (n = 13). Both LIBFR and HIWBFR groups trained for front leg and squat exercises 3 days per week for 3 weeks. Fasting growth hormone cortisol and testosterone levels were measured in the morning before and after exercise sessions. Data were analyzed with paired t-test and One-way ANOVA at the significant level of P < 0.05. Results: Serum cortisol level significantly increased after the exercise for both protocols compared to baseline (P < 0.05). After 3 weeks, serum cortisol level increased significantly in LIBFR and HIWBFR groups compared to control group (P < 0.001). At the end of the exercise protocols, serum testosterone level was higher in LIBFR group compared to HIWBFR group; however, this difference was not significant (P ˃ 0.49). Conclusions: Short term blood flow restriction (BFR) exercise stimulates cortisol hormones production in young men. However, this program seems too short to express any difference in testosterone change. Generally, it can be concluded that low-intensity resistance training can increase short-term BFR catabolic-anabolic hormones in young men.

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.

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.

Effect of Resistance Training on Intermuscular Adipose Tissue in Older Adults at Risk of Mobility Limitations

High levels of intermuscular adipose tissue (IMAT) in older adults are associated with muscle weakness and mobility limitations. This study determined if IMAT levels in older adults at risk of mobility limitations can be reduced following 12‐weeks of high‐load (HL)or low‐load blood flow restricted (BFR) resistance training. Twenty‐seven older adults (77.6 + 8.9 years; 27.3 +2.7 kg·m‐2) with low quadriceps muscle strength were randomly assigned to twice weekly sessions of HL (70% one repetition maximum, 1RM), BFR (30% 1RM coupled with a vascular restriction of 1.5 times systolic blood pressure at the proximal thigh) or attention control (CON) for 12‐weeks. HL and BFR groups engaged in three sets of leg extension, leg press, and leg curl training to muscular failure. The CON group performed light upper body resistance training that was not expected to result in muscle adaptations. T1 weighted magnetic resonance imaging scans were conducted to measure the volumes of skeletal muscle, subcutaneous adipose tissue (SAT), and IMAT in the thigh region before and after training. Following training, there were no differences in IMAT (P=0.22) and there were no differences in IMAT response between groups (P=0.38). SAT did not change over time (P=0.33) and there were no differences in SAT response between groups (P=0.39). Muscle volume significantly increased in the BFR group only (~5%; P=0.03) and was unchanged in the HL (~1.4%; P=0.18) and CON (~0.1; P=0.84). Twelve weeks of HL or BFR resistance training did not affect IMAT levels in older adults but it did improve muscle volume only after BFR training.Supported by NIH grant 1R15 A6040700‐01A1.

Blood flow restricted and traditional resistance training performed to fatigue produce equal muscle hypertrophy

This study investigated the hypertrophic potential of load-matched blood-flow restricted resistance training (BFR) vs free-flow traditional resistance training (low-load TRT) performed to fatigue. Ten healthy young subjects performed unilateral BFR and contralateral low-load TRT elbow flexor dumbbell curl with 40% of one repetition maximum until volitional concentric failure 3 days per week for 6 weeks. Prior to and at 3 (post-3) and 10 (post-10) days post-training, magnetic resonance imaging (MRI) was used to estimate elbow flexor muscle volume and muscle water content accumulation through training. Acute changes in muscle thickness following an early vs a late exercise bout were measured with ultrasound to determine muscle swelling during the immediate 0-48 h post-exercise. Total work was threefold lower for BFR compared with low-load TRT (P < 0.001). Both BRF and low-load TRT increased muscle volume by approximately 12% at post-3 and post-10 (P < 0.01) with no changes in MRI-determined water content. Training increased muscle thickness during the immediate 48 h post-exercise (P < 0.001) and to greater extent with BRF (P < 0.05) in the early training phase. In conclusion, BFR and low-load TRT, when performed to fatigue, produce equal muscle hypertrophy, which may partly rely on transient exercise-induced increases in muscle water content.

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.

Blood Flow Restriction Resistance Training

BLOOD FLOW RESTRICTION CAN BE USED IN RESISTANCE EXERCISE TO AUGMENT PHYSIOLOGICAL CHALLENGES AND STIMULATE ADAPTATIONS WHEN HEAVY LOADS ARE CONTRAINDICATED. FEMALE ATHLETES USING ONLY 20% 1 REPETITION MAXIMUM SUBSTANTIALLY IMPROVED THEIR MUSCULAR ENDURANCE, STRENGTH, HYPERTROPHY, AND MOTONEURON RECRUITMENT EFFICIENCY, WHEN TRAINING WAS COUPLED WITH LOCAL OCCLUSION OR EVEN WITH BREATHING HYPOXIC AIR.

Neuromuscular and Hypertrophic Adaptations to Short-term Blood Flow Restricted Resistance Training

Neuromuscular and Hypertrophic Adaptations to Short-term Blood Flow Restricted Resistance Training

Muscle Size And Arterial Stiffness After Blood Flow-restricted Elastic Band Resistance Training In Older Adults

Muscle Size And Arterial Stiffness After Blood Flow-restricted Elastic Band Resistance Training In Older Adults

Neuromuscular function following muscular unloading and blood flow restricted exercise

The aim of the study is to evaluate central and peripheral neuromuscular function in the knee extensors (KE) and plantar flexors (PF) after 30days of unilateral lower limb suspension (ULLS) and to examine the effects of low-load blood flow restricted (BFR) resistance training on the KE during ULLS. Strength, cross-sectional area (CSA), central activation, evoked force, and rates of force development and relaxation were assessed in the KE and PF before and after ULLS in sixteen subjects (9M, 7F; 18-49years). Eight of those subjects participated in BFR on the KE three times per week during ULLS (ULLS+Exercise). The ULLS group had decrements in strength and CSA of the KE (16 and 7%, respectively) and PF (27 and 8%, respectively) and the ULLS+Exercise maintained strength and CSA of the KE (P>0.05), but significantly lost strength andCSA in the PF (21 and 5%; P>0.05). KE central activation declined 6% in the ULLS group and was maintained in the ULLS+Exercise group, but a time×group interaction was not evident (P=0.31). PF central activation was reduced in both groups (ULLS: -7.6±9.9 and -7.9±11.6%; time main effect P=0.01). A time×group interaction for KE-evoked twitch force (P=0.04) demonstrated a 9% decline in the ULLS+Exercise group following the intervention. Evoked PF doublet torque decreased 12% in both groups (P=0.002). Central and peripheral neuromuscular function is compromised during unloading. While BFR resistance training on the KE during unloading can maintain muscle mass and strength, it may only partially attenuate neuromuscular dysfunction.

Vascular adaptations to low-load resistance training with and without blood flow restriction

To examine the effects of low-load knee extensor training to fatigue with and without blood flow restriction (BFR) on calf vascular conductance, calf venous compliance, and peripheral arterial stiffness in middle-aged individuals. Eleven men (55 ± 8 years) and five post-menopausal women (57 ± 5 years) completed 6 weeks of unilateral knee extensor training with one limb exercising with BFR (BFR limb) and the contralateral limb exercising without BFR (free flow, FF limb). Before and after the training, femoral pulse wave velocity (PWV), calf blood flow (normalized as conductance), and calf venous compliance were measured in each limb. PWV increased following training in both limbs (main effect of time, p = 0.036; BFR limb 8.9 ± 0.8 vs. 9.5 ± 0.9 m/s, FF limb 9.0 ± 1.2 vs. 9.0 ± 1.1; Pre vs. Post). Calf blood flow increased (p = 0.026) in the FF limb (25.0 ± 7.0 vs. 31.8 ± 12.0 flow/mmHg; Pre vs. Post) but did not change (p = 0.831) in the BFR limb (29.1 ± 11.3 vs. 28.7 ± 11.5 flow/mmHg; Pre vs. Post). Calf venous compliance did not change in either limb following training. These results suggest low-load BFR resistance training to fatigue elicits small increases in peripheral arterial stiffness without eliciting concomitant changes in venous compliance. In addition, unlike low-load knee extensor training without BFR, training with BFR did not enhance calf blood flow.

Perceptual effects and efficacy of intermittent or continuous blood flow restriction resistance training

Blood flow restriction (BFR) exercise may be an alternative form of resistance training; however, a side of effect of BFR resistance exercise is acute muscle pain. Typically, BFR exercise studies restrict blood flow with a cuff continuously during the exercise bout, including rest periods. However, others have used intermittent BFR where the cuff is inflated only during sets. We performed two studies to compare intermittent and continuous BFR exercise. In study one, eleven subjects randomly proceeded through three treatments of unilateral leg extensions to failure: (i) continuous BFR, (ii) intermittent BFR and (iii) control (exercise without BFR). Pain measurements were taken immediately after each set. In study two, subjects (n = 32) underwent a 5-week resistance training programme after random assignment to one of the three conditions. Lean mass and strength were assessed at baseline and after training. Continuous BFR resulted in significantly greater pain than intermittent BFR or control. Both BFR conditions resulted in significantly fewer repetitions to failure than control. This suggests that an acute bout of intermittent BFR exercise may produce as much muscle fatigue as an acute bout of continuous BFR exercise, but with less pain. With training, maximal knee extension (P = 0·033) and maximum knee flexion (P = 0·007) strength increased among all groups. There were no significant differences between groups in strength or lean mass. These results suggest that short-term low-load resistance training increases muscle strength to a similar extent as low-load resistance training without BFR.

Effects of low-intensity concentric and eccentric exercise combined with blood flow restriction on indices of exercise-induced muscle damage

Low-intensity blood-flow restriction (BFR) resistance training significantly increases strength and muscle size, but some studies report it produces exercise-induced muscle damage (EIMD) in the lower body after exercise to failure. To investigate the effects of a pre-set number of repetitions of upper body concentric and eccentric exercise when combined with BFR on changes in EIMD. Ten young men had arms randomly assigned to either concentric BFR (CON-BFR) or eccentric BFR (ECC-BFR) dumbbell curl exercise (30% one-repetition maximum (1-RM), 1 set of 30 repetitions followed by 3 sets of 15 repetitions). Maximal isometric voluntary contraction force (MVC), muscle thickness (MTH), circumference, range of motion (ROM), ratings of perceived exertion (RPE), and muscle soreness were measured before, immediately after, and daily for 4 days post-exercise. MVC decreased by 36% for CON-BFR and 12% for ECC-BFR immediately after exercise but was not changed 1-4 days post-exercise (p > 0.05). Only CON-BFR had significant changes in MTH and circumference immediately after exercise (p < 0.05). Muscle soreness was observed in the ECC-BFR arm at 1 and 2 days after exercise. Low-intensity ECC-BFR produces significant muscle soreness at 24 h but neither ECC-BFR nor CON-BFR exercise produces significant changes in multiple indices of EIMD.

Cross-over Muscular Adaptation to Blood Flow–Restricted Exercise

Dear Editor-in-Chief: We read with interest the article published by Weatherholt et al. (7). The authors performed a well-controlled study that adds to our knowledge about blood flow–restricted exercise. With their within-subject design, the authors observed similar increases in upper arm muscle cross-sectional area (mCSA) and strength after 8 wk of low load unilateral elbow flexion and extension training with and without blood flow restriction (BFR). The authors suggest that the adaptations for both muscle strength and hypertrophy observed in the limb trained without BFR are attributable to a cross-education effect. Although unilateral training with a high load can increase muscular strength in the untrained, contralateral limb (6), we feel it is likely that the training adaptations observed in the limb trained without BFR are due to the local training stimulus itself. The authors’ reason for suggesting a neural cross-education effect is that training with a low load “is generally accepted as being too low to cause strength increases” (7). Although evidence suggests that high-load training does produce greater increases in strength compared with low-load training, it is clear that low-load training will increase maximal strength to an extent (1). Moreover, other studies using a within-subject design have shown greater increases in muscular strength in a limb trained under BFR compared with the contralateral limb trained without BFR (5). This suggests that increases in strength in one limb are not always equivalent in the contralateral limb. The similar increases in muscular strength observed in both the BFR- and non–BFR-trained limb in the present study are likely attributable to similar increases in mCSA (7). With respect to the author’s second conclusion, a systemic effect of BFR resistance training causing anabolic hormone-induced hypertrophy of the contralateral limb, we suggest that the increase in mCSA of the non–BFR-trained limb is likely due to the local training stimulus itself. Although BFR knee extensor and flexor exercise has been shown to enhance training-induced hypertrophy of the elbow flexors (3), the acute anabolic hormonal response causing such adaptation is questionable. In contrast to the aforementioned study, West et al. (8) have shown that exercise-induced increases in anabolic hormones do not enhance training-induced hypertrophy of the elbow flexors. Furthermore, elbow flexor exercise alone is unable to cause an acute rise in such hormones (8). In the present investigation (7), it is unlikely that such a low volume of unilateral elbow flexor and extensor exercise, even with BFR, would be able to increase such hormones. It is likely that 8 wk of low-load training without BFR was capable of inducing muscle hypertrophy because low-load training without BFR has been shown previously to induce muscle hypertrophy (2,4). This commentary should not be taken as criticism of the study; we offer another possible explanation for the muscular adaptations observed with low-load training without BFR. Similar training adaptations to different unilateral training protocols should not necessarily be attributed to a cross-over effect. C.A. Fahs has received a grant from the American College of Sports Medicine for doctoral research in Kaatsu methodology (#012012).

Effects of Blood Flow Restricted Low-Intensity Concentric or Eccentric Training on Muscle Size and Strength

We investigated the acute and chronic effects of low-intensity concentric or eccentric resistance training with blood flow restriction (BFR) on muscle size and strength. Ten young men performed 30% of concentric one repetition maximal dumbbell curl exercise (four sets, total 75 reps) 3 days/week for 6 weeks. One arm was randomly chosen for concentric BFR (CON-BFR) exercise only and the other arm performed eccentric BFR (ECC-BFR) exercise only at the same exercise load. During the exercise session, iEMG for biceps brachii muscles increased progressively during CON-BFR, which was greater (p<0.05) than that of the ECC-BFR. Immediately after the exercise, muscle thickness (MTH) of the elbow flexors acutely increased (p<0.01) with both CON-BFR and ECC-BFR, but was greater with CON-BFR (11.7%) (p<0.01) than ECC-BFR (3.9%) at 10-cm above the elbow joint. Following 6-weeks of training, MRI-measured muscle cross-sectional area (CSA) at 10-cm position and mid-upper arm (12.0% and 10.6%, respectively) as well as muscle volume (12.5%) of the elbow flexors were increased (p<0.01) with CON-BFR. Increases in muscle CSA and volume were lower in ECC-BFR (5.1%, 0.8% and 2.9%, respectively) than in the CON-BFR and only muscle CSA at 10-cm position increased significantly (p<0.05) after the training. Maximal voluntary isometric strength of elbow flexors was increased (p<0.05) in CON-BFR (8.6%), but not in ECC (3.8%). These results suggest that CON-BFR training leads to pronounced acute changes in muscle size, an index of muscle cell swelling, the response to which may be an important factor for promoting muscle hypertrophy with BFR resistance training.

Blood flow‐restricted resistance exercise: rapidly affecting the myofibre and the myonuclei

Acute blood flow restriction (BFR) by itself or in combination with low-intensity aerobic and/or low-load resistance exercise has been shown to result in favourable effects on skeletal muscle, namely increases in muscle size and strength (Loenneke et al. 2012). These positive muscular adaptations have been observed across a wide range of populations (e.g. athletes, elderly, diseased). Previous research indicates that BFR resistance exercise stimulates muscle protein synthesis (MPS) (Gundermann et al. 2012); however, little is known about the exact cellular mechanisms behind that response on muscle protein synthesis or muscle hypertrophy. Previous research suggests that the muscle hypertrophic effect may, in part, be related to the concomitant decrease in the mRNA gene expression of E3-ligases such as MURF-1 (8 h post-decrease; Manini et al. 2011) and atrogin (Manini et al. 2011). Furthermore, Laurentino et al. (2012) have observed decreased mRNA gene expression of myostatin, with an increased expression of the follistatin isoforms following low-load resistance exercise with BFR. In a recent issue of The Journal of Physiology, Nielsen et al. (2012) presented research that suggests that the proliferation of myogenic stem cells may be an additional mechanism involved in the muscle hypertrophic response to high-frequency low-load resistance exercise with BFR. Briefly, participants performed four sets of knee extensor exercise to failure at 20% of their concentric one repetition maximum. The researchers found that performing 23 sessions of low-load BFR exercise within 19 days resulted in marked increases in muscular strength and muscle fibre cross-sectional area when measured greater than 3 days post-training. It should be mentioned that there were transient increases in muscle fibre cross-sectional area after 5 days of the intervention in both groups; however, this was thought to be due to exercise-induced cell swelling and not a reflection of true muscle hypertrophy. This is supported by the post-training data which indicated increases in muscle size and strength only in the BFR group, while the work-matched control groups’ fibre cross-sectional area was equivalent to baseline levels. These positive muscular adaptations in the BFR group were accompanied by a substantial upregulation in myogenic stem cells, resulting in nuclear additions to the exercised muscle fibre. The data reported in the Nielsen et al. (2012) investigation provides valuable insight into the acute and chronic effects of high-frequency low-load resistance training with BFR. The increased proliferation of myogenic stem cells with BFR resistance training is significant as it is thought that the myonuclear donation is required in order to have substantial increases in human muscle fibre cross-sectional area. Further support of this notion comes from their data which show positive correlations between the change in myonuclei number per fibre and muscle fibre area as well as between the relative change in myogenic stem cells per fibre and muscle fibre area. The exact reason behind the large increase in myogenic stem cell proliferation is not known, but the authors speculated that the activation and proliferation of myogenic stem cells may be acutely stimulated by BFR-induced stretch-, hypoxia-, and/or contraction-induced nitric oxide secretion. In addition, they noted that it was unlikely that the increased proliferation was due to muscle cell membrane damage because the authors did not find any visible signs of damage to the basal lamina from their laminin stainings. This finding is consistent with previous BFR studies, which indicate minimal to no muscle damage with this type of exercise. It would be interesting if future research could expand on these findings and investigate whether or not there is proliferation of myogenic stem cells and a subsequent myonuclear addition in response to low-intensity aerobic exercise in combination with BFR. This type of study would be useful as low-intensity aerobic exercise with BFR has been observed to elicit significant increases in muscle size and strength (Loenneke et al. 2012). Currently it is unknown if the mechanisms behind that effect are different to that observed with low-load resistance training. Additionally, BFR in the absence of exercise has been shown to attenuate atrophy; however, it is unclear as to the exact mechanism involved with BFR in the absence of muscle contraction. Whether or not there is a relationship between the application of BFR in the absence of muscle contraction and myogenic stem cells is unknown but might be an interesting avenue of research to explore in the future.

Effects of high-intensity and blood flow-restricted low-intensity resistance training on carotid arterial compliance: role of blood pressure during training sessions

We examined the effects of high-intensity resistance training (HIT) and low-intensity blood flow-restricted (LI-BFR) resistance training on carotid arterial compliance. Nineteen young men were randomly divided into HIT (n = 9) or LI-BFR (n = 10) groups. The HIT and LI-BFR groups performed 75 and 30 %, respectively, of one-repetition maximum (1-RM) bench press exercise, 3 days per week for 6 weeks. During the training sessions, the LI-BFR group wore elastic cuffs around the most proximal region of both arms. Muscle cross-sectional area (CSA), 1-RM strength, and carotid arterial compliance were measured before and 3 days after the final training session. Acute changes in systolic arterial pressure (SAP), plasma endothelin-1 (ET-1), nitrite/nitrate (NOx), and noradrenalin concentrations were also measured during and after a bout of training session. The training led to significant increases (P < 0.01) in bench press 1-RM and arm and chest muscle CSA in the two training groups. Carotid arterial compliance decreased significantly (P < 0.05) in the HIT group, but not in the LI-BFR group. There was a significant correlation (r = -0.533, P < 0.05) between the change in carotid arterial compliance and the acute change in SAP during training sessions; however, ET-1 and NOx did not correlate with carotid arterial compliance. Our results suggest that muscle CSA and strength increased following 6 weeks of both HIT and LI-BFR training. However, carotid arterial compliance decreased in only the HIT group, and the changes were correlated with SAP elevations during exercise sessions.

Rehabilitation of an osteochondral fracture using blood flow restricted exercise: A case review

ObjectivesIn this case review we report on a bodybuilder who used a practical model of blood flow restriction (BFR) training to successfully rehabilitate himself following an injury to his right knee. ResultsThe patient originally thought he had torn his meniscus however repeat radiographs and magnetic resonance imaging (MRI) confirmed an osteochondral fracture. The patient initially sought out a low load alternative to help with the maintenance of skeletal muscle mass. However, following rehabilitation with low load BFR resistance training, radiographs indicated that the bone had begun to heal suggesting that this type of training may also benefit bone. ConclusionsIn conclusion, this case review provides evidence that practical BFR using knee wraps can serve as an effective stimulus during rehabilitation from a knee injury.