Leg Blood Flow Restriction Research Articles

Leg Blood Flow During Exercise with Blood Flow Restriction: Evidence for and Implications of Compensatory Cardiovascular Mechanisms.

Proximal limb cuff inflation to 40% arterial occlusion pressure (AOP) is assumed to reduce exercising leg perfusion, creating "blood flow restriction" (BFR). However, no study has validated this assumption. 18 healthy young participants (9F) performed two-legged knee flexion/extension exercise at 25% WRpeak with bilateral cuffs applied to the proximal thigh at 0% AOP (CTL), 20% AOP and 40% AOP. Leg blood flow (LBF; Doppler and echo ultrasound) and cardiac output (CO; finger photoplethysmography) were measured during rest and exercise. LBF values were doubled to account for both exercising legs. 20% and 40% AOP reduced exercising LBF in a dose-response manner (P<.01). However, the magnitude of the leg blood flow restriction by 40% AOP was progressively attenuated across the exercise bout (5-15s: 37%, 50-70s: 20%, 240-300s: 16%; P<.01) due to compensatory increases in leg vascular conductance (LVC) (P<.01). Between 5-15s of exercise, 40% AOP significantly reduced CO compared to CTL and 20% AOP (8.0 ± 1.3 vs. 8.4 ± 1.5 L/min, P<.001 and 8.5 ± 1.5, P<.001). By 240-300s, there were no significant differences in CO between cuff pressures (all P>.13). Pneumatic cuff inflation at 20% and 40% AOP reduces LBF in a dose-response manner, but this impairment was progressively attenuated across the exercise bout by an increase in LVC. Importantly, this compensatory response differed across participants, which may have implications for the degree of adaptations following BFR training. Furthermore, restoration of normal CO during BFR despite compromised limb perfusion suggests other tissue perfusion is increased as part of the response.

Dual-task improvement of older adults after treadmill walking combined with blood flow restriction of low occlusion pressure: the effect on the heart–brain axis

ObjectiveThis study explored the impact of one session of low-pressure leg blood flow restriction (BFR) during treadmill walking on dual-task performance in older adults using the neurovisceral integration model framework.MethodsTwenty-seven older adults participated in 20-min treadmill sessions, either with BFR (100 mmHg cuff pressure on both thighs) or without it (NBFR). Dual-task performance, measured through light-pod tapping while standing on foam, and heart rate variability during treadmill walking were compared.ResultsFollowing BFR treadmill walking, the reaction time (p = 0.002) and sway area (p = 0.012) of the posture dual-task were significantly reduced. Participants exhibited a lower mean heart rate (p < 0.001) and higher heart rate variability (p = 0.038) during BFR treadmill walking. Notably, BFR also led to band-specific reductions in regional brain activities (theta, alpha, and beta bands, p < 0.05). The topology of the EEG network in the theta and alpha bands became more star-like in the post-test after BFR treadmill walking (p < 0.005).ConclusionBFR treadmill walking improves dual-task performance in older adults via vagally-mediated network integration with superior neural economy. This approach has the potential to prevent age-related falls by promoting cognitive reserves.

Effects of blood flow restriction on mechanical properties of the rectus femoris muscle at rest.

Introduction: This study examined the effects of blood flow restriction (BFR) and reperfusion on the mechanical properties of the rectus femoris muscle at rest (frequency and stiffness). Methods: Fourteen trained men (body weight = 81.0 ± 10.3kg; BMI = 25 ± 3.0m/kg2; height = 181 ± 4cm; training experience = 6.0 ± 2.2years) participated in an experimental session involving their dominant (BFR) and non-dominant leg (control). Muscle mechanical properties were measured using Myoton's accelerometer at the midpoint of the rectus femoris muscle at five time points. In the BFR leg, an 80% arterial occlusion pressure was applied by a cuff for 5min. No cuff was applied in the control leg. Femoral Myoton measurements were taken from both legs 2 and 4min after the start of BRF as well as 30s and 2min after the end of the occlusion period. Results: The two-way ANOVA revealed a statistically significant interaction effect for stiffness and frequency (p < 0.001; η2 > 0.67). The post hoc analysis showed that both stiffness and frequency increased during BFR compared with rest and then dropped to the resting levels post BFR period. Also, stiffness and frequency were higher than control only during the BFR period, and similar during rest and post BFR. Conclusion: These results indicate that the application of BFR at rest leads to significant changes in mechanical properties of the rectus femoris muscle.

Walking With Leg Blood Flow Restriction: Wide-Rigid Cuffs vs. Narrow-Elastic Bands.

BackgroundBlood flow restriction (BFR) training is becoming a popular form of exercise. Walking exercise in combination with pressurized wide-rigid (WR) cuffs elicits higher cardiac workload and a vascular dysfunction due presumably to reperfusion injury to the endothelium. In contrast, narrow-elastic (NE) BFR bands may elicit different hemodynamic effects. Therefore, we compared the acute cardiovascular responses to two distinct forms of BFR training during light-intensity exercise.Methods and Results15 young healthy participants (M = 9, F = 6) performed five bouts of 2-min walking intervals at 0.9 m/s with a 1-min rest and deflation period with either WR, NE, or no bands placed on upper thighs. Cuff pressure was inflated to 160 mmHg in WR cuffs and 300 mmHg in NE bands while no cuffs were used for the control. Increases in heart rate and arterial blood pressure were greater (p < 0.05) in the WR than the NE and control conditions. Double product increased to a greater extent in the WR than in the NE and control conditions. Increases in perceived exertion and blood lactate concentration were greater (p < 0.05) in the WR compared with the NE and control conditions (p < 0.05), while no differences emerged between the NE and control conditions. There were no changes in arterial stiffness or brachial artery flow-mediated dilation (FMD) after all three trials.ConclusionUse of WR BFR cuffs resulted in a marked increase in blood pressure and myocardial oxygen demand compared with NE BFR bands, suggesting that NE bands present a safer alternative for at-risk populations to perform BFR exercise.Clinical Trial RegistrationThis study was registered in the Clinicaltrials.gov (NCT03540147).

Walking With Leg Blood Flow Restriction: Wide-rigid Cuffs Vs. Narrow-elastic Bands

Walking With Leg Blood Flow Restriction: Wide-rigid Cuffs Vs. Narrow-elastic Bands

Blood Flow Restriction During Futsal Training Increases Muscle Activation and Strength

The aim of this study was to investigate the effect of leg blood flow restriction (BFR) applied during a 3-a-side futsal game on strength-related parameters. Twelve male futsal players were randomly assigned into two groups (n = 6 for each group) during 10 training sessions either with or without leg BFR. Prior to and post-training sessions, participants completed a series of tests to assess anabolic hormones and leg strength. Pneumatic cuffs were initially inflated to 110% of leg systolic blood pressure and further increased by 10% after every two completed sessions. In comparison with baseline, the resting post-training levels of myostatin (p = 0.002) and IGF-1/MSTN ratio (p = 0.006) in the BFR group changed, whereas no change in the acute level of IGF-1 and myostatin after exercise was observed. Peak torque of knee extension and flexion increased in both groups (p < 0.05). A trend of increased neural activation of all heads of the quadriceps was observed in both groups, however, it was statistically significant only for rectus femoris in BFR (p = 0.02). These findings indicated that the addition of BFR to normal futsal training might induce greater neuromuscular benefits by increasing muscle activation and augmenting the hormonal response.

Blood Flow Restriction Only Increases Myofibrillar Protein Synthesis with Exercise.

Combining blood flow restriction (BFR) with exercise can stimulate skeletal muscle hypertrophy. Recent observations in an animal model suggest that BFR performed without exercise can also induce anabolic effects. We assessed the effect of BFR performed both with and without low-load resistance-type exercise (LLRE) on in vivo myofibrillar protein synthesis rates in young men. Twenty healthy young men (age = 24 ± 1 yr, body mass index = 22.9 ± 0.6 kg·m) were randomly assigned to remain in resting condition (REST ± BFR; n = 10) or to perform LLRE (LLRE ± BFR at 20% one-repetition maximum; n = 10), combined with two 5-min cycles of single leg BFR. Myofibrillar protein synthesis rates were assessed during a 5-h post-BFR period by combining a primed continuous L-[ring-C6]phenylalanine infusion with the collection of blood samples, and muscle biopsies from the BFR leg and the contralateral control leg. The phosphorylation status of anabolic signaling (mammalian target of rapamycin pathway) and metabolic stress (acetyl-CoA carboxylase)-related proteins, as well as the mRNA expression of genes associated with skeletal muscle mass regulation, was assessed in the collected muscle samples. Under resting conditions, no differences in anabolic signaling or myofibrillar protein synthesis rates were observed between REST + BFR and REST (0.044% ± 0.004% vs 0.043% ± 0.004% per hour, respectively; P = 0.683). By contrast, LLRE + BFR increased myofibrillar protein synthesis rates by 10% ± 5% compared with LLRE (0.048% ± 0.005% vs 0.043% ± 0.004% per hour, respectively; P = 0.042). Furthermore, compared with LLRE, LLRE + BFR showed higher phosphorylation status of acetyl-CoA carboxylase and 4E-BP1 as well as the elevated mRNA expression of MuRF1 (all P < 0.05). BFR does not increase myofibrillar protein synthesis rates in healthy young men under resting conditions. When combined with LLRE, BFR increases postexercise myofibrillar protein synthesis rates in vivo in humans.

Mild aerobic training with blood flow restriction increases the hypertrophy index and MuSK in both slow and fast muscles of old rats: Role of PGC-1α

AimsExisting evidence emphasize the role of mitochondrial dysfunction in sarcopenia which is revealed as loss of skeletal muscle mass and neuromuscular junction remodeling. We assessed the effect of low-intensity aerobic training along with blood flow restriction on muscle hypertrophy index, muscle-specific kinase (MuSK), a pivotal protein of the neuromuscular junction and Peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) in aged male rats. Main methodsAnimals groups were control (CTL), sham (Sh), leg blood flow restriction (BFR), exercise (Ex), sham + exercise (Sh + Ex), and BFR plus exercise (BFR + Ex) groups. The exercise groups were trained with low intensity exercise for 10 weeks. 48 h after the last training session, animals were sacrificed under anesthesia. Soleus and EDL muscles were isolated, hypertrophy index was estimated and MuSK and PGC-1α were measured by western blot method. Key findingsHypertrophy index enhanced in soleus and Extensor digitorum longus (EDL) muscles of BFR + Ex group (P < 0.01 versus CTL and Sh groups, and P < 0.001 versus other groups). The MuSK protein of soleus and EDL muscles increased in BFR + Ex group (P < 0.01 and P < 0.001, respectively) in comparison with CTL and Sh groups. In BFR + Ex group, the PGC-1α protein increased in both soleus and EDL (P < 0.001 compared to other groups). Also the PGC-1α of soleus muscle was higher in Ex and Sh + Ex groups versus CTL and Sh groups (P < 0.05). SignificanceFindings suggest that low endurance exercise plus BFR improves the MuSK and hypertrophy index of both slow and fast muscles of elderly rats probably through the rise of PGC-1α expression.

Effect of Leg Blood Flow Restriction during Cycling on Cerebral Perfusion: Role of Carbon Dioxide

Exercise with blood flow restriction (BFR) enhances skeletal muscle metabolite accumulation and has been used to stimulate training‐induced improvements in strength and endurance, but the consequences for the cerebral circulation are unknown. The activation of group III and IV skeletal muscle afferents by exercise‐induced metabolites (muscle metaboreflex) has been suggested to increase cerebral perfusion during exercise. However, this may be masked by a hyperventilation related decrease in the partial pressure of arterial carbon dioxide (indexed by partial pressure of end‐tidal carbon dioxide; PETCO2). We sought to determine how muscle metaboreflex activation with BFR affects cerebral blood flow and whether this is secondary to confounding changes in PETCO2. In 11 healthy male participants (age 25±4 years; height 180±1 cm; weight 71±7 kg; mean±SD) we measured middle cerebral artery mean blood velocity (MCAVm), internal carotid artery blood flow (ICAQ) and PETCO2, during leg cycling exercise under free‐flow conditions (target heart rate at 120 bpm) and with BFR. Trials were conducted where PETCO2 was permitted to fluctuate spontaneously (control) and where PETCO2 was clamped at 1 mmHg above resting levels. In the control trial, PETCO2 was slightly increased from rest during leg cycling (Δ2.2±0.3 mmHg; P&lt;0.05) and significantly decreased during exercise with BFR (Δ‐4.8±0.9 mmHg; P&lt;0.05). PETCO2 remained unchanged throughout the clamp trial. Leg cycling under free‐flow conditions evoked similar increases in MCAVm during the control (Δ6.5±1.8 cm.s−1) and PETCO2 clamp (Δ6.8±2.4 cm.s−1) trials (P&lt;0.05 vs. rest). During exercise with BFR a further increase in MCAVm was noted in the PETCO2 clamp trial (Δ5.9±1.4 cm.s−1; P&lt;0.05 vs. rest and free‐flow exercise), but not in the control trial. In both trials, ICAQ was not significantly changed from rest during leg cycling under free‐flow conditions (control Δ‐3.5±10.31 ml.min−1; PETCO2 clamp Δ7.2±7.41 ml.min−1; P&gt;0.05 vs. rest). During exercise with BFR, ICAQ was significantly increased when PETCO2 was clamped (Δ27.2±6.6 ml.min−1; P&lt;0.05 vs. rest), but was decreased in the control trial (Δ‐22.7±12.1 ml.min−1; P&lt;0.05 vs. rest). In conclusion, enhanced muscle metaboreflex activation with leg BFR during cycling increases cerebral blood flow, but only when PETCO2 is maintained at resting levels.Support or Funding InformationThis study was supported by Coordination for the Improvement of Higher Education Personnel (CAPES‐Brazil) through the program Science without Borders.

The Effect of Stair Exercise with Restriction Blood Flow on Knee Extensor Muscle

PURPOSE: Low-intensity exercise with restriction of blood flow has been proposed as an alternative exercise to secure the disadvantage of a high-intensity resistance exercise. However, studies of how affects the muscle using functional exercise are lacking. Thus, the purpose of this study was to investigate knee extensor muscle strength during stair exercise of functional exercise with leg blood flow restriction. METHODS: Twenty two healthy young adults with no history of musculoskeletal or neurogical disorder were participated in this study. participant were randomized into either non-restriction group(11 subject) or restriction group (11 subject). The restriction blood cuff attached to the proximal end of the leg. Measurement of knee extensor strength was used by cybex dynamometer. Data analyzed in independent t-test and paired t-test. RESULTS: Knee extensor muscle strength was significantly different between groups. Also, there were significant differences in the strength of knee extensor within the group. CONCLUSION: This study found that stair exercise with restriction of blood flow did influence to knee extensor muscle strength. These results will also be able to promote the effect of increasing the muscle power applied to functional exercise. Henceforth, studies will be made in the intervention method that can be applied to health vulnerable person.

Impact of leg blood flow restriction during walking on central arterial hemodynamics.

Walking exercise with limb blood flow restriction (BFR) has been shown to increase muscular mass and strength even if it is performed at low exercise intensities. Despite mounting evidence for its efficacy and the increasing popularity, the safety of BFR exercise in relation to cardiac loads has not been established. The aim of this study was to determine the response of central hemodynamics during the BFR exercise to assess its impact on cardiac load. Fifteen apparently healthy sedentary or recreationally active adults (10 men and 5 women, 27 ± 1 yr) underwent five bouts of 2-min constant treadmill walking at 2 mph with 1-min rest intervals either with or without BFR on both proximal thighs. Beat-by-beat blood pressure and hemodynamics (via Modelflow method) were measured, and central arterial hemodynamics were evaluated with pulse wave analyses via general transfer function. Incident wave amplitude (IWA) and reflected wave amplitude (RWA) were obtained by the wave separation analysis. Peripheral systolic blood pressure (SBP) increased more substantially during walking with BFR (43 ± 5% vs. baseline) than without BFR (11 ± 4% vs. baseline). Aortic SBP did not change significantly during walking without BFR, but there was a substantial elevation in aortic SBP (43 ± 5% vs. baseline) during walking with BFR. Significant effect of BFR was seen in IWA but not in RWA. These findings suggest that even during slow-speed walking, leg BFR induces substantial hypertensive responses in the aorta. However, this response could not be explained by the augmented wave reflection.

Impact of Walking with Leg Blood Flow Restriction on Central Blood Pressure and Subendocardial Viability

PURPOSE: Walking exercise with limb blood flow restriction (BFR) has been shown to increase muscular mass and strength even if it is performed at low intensities. Despite mounting evidence for its efficacy and the increasing popularity, the safety of BFR exercise in relation to cardiac loads has not been established. We measured central blood pressure in order to more accurately assess blood pressure load imposed on the left ventricle during the BFR exercise. Additionally, as restricted venous return expectedly induced smaller increase in stroke volume and greater tachycardia (i.e., shorter diastolic duration), subendocardial viability ratio, an index of myocardial perfusion relative to left ventricular workload, was derived. METHODS: Fifteen apparently healthy adults (10 men and 5 women, 27±1 years) underwent five bouts of 2-minute treadmill walking at 2 miles/hour with 1-min interval either with or without BFR on both proximal thighs. Beat-by-beat peripheral blood pressure and hemodynamics were measured using the Portapres. Central arterial hemodynamics was evaluated with pulse wave analysis via general transfer function. RESULTS: Peripheral systolic blood pressure (SBP) increased during walking more substantially with BFR (43±5% vs. baseline) than without during BFR (12±4% vs. baseline). Although aortic SBP did not change significantly during walking without BFR, there was a substantial elevation in aortic SBP during walking with BFR (41±4% vs. baseline). Compared with the non-BFR session, significantly smaller increase in stroke volume and shorter diastolic duration were observed during the BFR session. Thus, despite greater hypertensive response, subendocardial viability ratio was significantly lower in the BFR session compared with the non-BFR session (P<0.05). CONCLUSIONS: These findings suggest that even during slow-speed walking, leg BFR induces a greater hypertensive response in the aorta and a lower myocardial perfusion. These central hemodynamic responses might force a circulatory challenge, particularly for those with compromised cardiovascular function.

Acute low-load resistance exercise with and without blood flow restriction increased protein signalling and number of satellite cells in human skeletal muscle

To investigate hypertrophic signalling after a single bout of low-load resistance exercise with and without blood flow restriction (BFR). Seven subjects performed unilateral knee extensions at 30 % of their one repetition maximum. The subjects performed five sets to failure with BFR on one leg, and then repeated the same amount of work with the other leg without BFR. Biopsies were obtained from m. vastus lateralis before and 1, 24 and 48 h after exercise. At 1-h post-exercise, phosphorylation of p70S6KThr389 and p38MAPKThr180/Tyr182 was elevated in the BFR leg, but not in the free-flow leg. Phospho-p70S6KThr389 was elevated three- to fourfold in both legs at 24-h post-exercise, but back to baseline at 48 h. The number of visible satellite cells (SCs) per muscle fibre was increased for all post-exercise time points and in both legs (33–53 %). The proportion of SCs with cytoplasmic extensions was elevated at 1-h post in the BFR leg and the number of SCs positive for myogenin and/or MyoD was increased at 1- and 24-h post-exercise for both legs combined. Acute low-load resistance exercise with BFR resulted in early (1 h) and late (24 h) enhancement of phospho-p70S6KThr389, an early response of p38MAPK, and an increased number of SCs per muscle fibre. Enhanced phospho-p70S6KThr389 at 24-h post-exercise and increases in SC numbers were seen also in the free-flow leg. Implications of these findings for the hypertrophic effects of fatiguing low-load resistance exercise with and without BFR are discussed.

Cardiovascular drift during low intensity exercise with leg blood flow restriction

Previous studies reported that aerobic-type exercise such as walking or cycling with blood flow restriction (BFR) has been shown to elicit increases in leg muscle hypertrophy and strength, as well as improved aerobic capacity. Although previous studies investigated cardiovascular responses during a relatively short duration of exercise (∼5 min), the effects of prolonged leg muscular BFR have remained unknown. The purpose of this study was to examine the cardiovascular effects of longer duration low intensity exercise combined with BFR. Eight men performed 30 min of exercise at 40% of a predetermined maximal oxygen uptake under both BFR and normal flow (CON) conditions. Cardiovascular parameters were measured at rest and every 10 min during exercise. The main findings were that 1) the SV and HR did not change significantly between 10 to 30 min of exercise in BFR and CON conditions, although BFR-induced reduction of SV and increased HR were found at 10 min exercise compared with normal flow, 2) blood pressure was increased at 10 min of exercise in BFR compared to the CON, however the blood pressure decreased gradually with BFR from 10 to 30 min of exercise, and 3) blood lactate and RPE increased gradually during exercise with BFR. In conclusion, our results suggest that the BFR-induced reduction of SV and increased HR within the first 10 min of exercise are representative of changes in these parameters.

Exercise intensity and muscle hypertrophy in blood flow–restricted limbs and non‐restricted muscles: a brief review

Although evidence for high-intensity resistance training-induced muscle hypertrophy has accumulated over the last several decades, the basic concept of the training can be traced back to ancient Greece: Milo of Croton lifted a bull-calf daily until it was fully grown, which would be known today as progressive overload. Now, in the 21st century, different types of training are being tested and studied, such as low-intensity exercise combined with arterial as well as venous blood flow restriction (BFR) to/from the working muscles. Because BFR training requires the use of a cuff that is placed at the proximal ends of the arms and/or legs, the BFR is only applicable to limb muscles. Consequently, most previous BFR training studies have focused on the physiological adaptations of BFR limb muscles. Muscle adaptations in non-BFR muscles of the hip and trunk are lesser known. Recent studies that have reported both limb and trunk muscle adaptations following BFR exercise training suggest that low-intensity (20-30% of 1RM) resistance training combined with BFR elicits muscle hypertrophy in both BFR limb and non-BFR muscles. However, the combination of leg muscle BFR with walk training elicits muscle hypertrophy only in the BFR leg muscles. In contrast to resistance exercise with BFR, the exercise intensity may be too low during BFR walk training to cause muscle hypertrophy in the non-BFR gluteus maximus and other trunk muscles. Other mechanisms including hypoxia, local and systemic growth factors and muscle cell swelling may also potentially affect the hypertrophic response of non-BFR muscles to BFR resistance exercise.

Time course changes in muscle size and fatigue during walking with restricted leg blood flow in young men

Walk training combined with blood flow restriction (BFR) leads to hypertrophic effects in leg muscle, but the underlying physiological mechanisms are poorly understood. We examined the time course of the acute effects of BFR slow walk (BFR-slow; walking speed 56 m/min), BFR fast walk (BFR-fast; walking speed 87 m/min), and control walk (CON-slow; walking speed 56 m/min) on ultrasound-measured muscle thickness (MTH) and on isometric knee extension strength in 8 young men. No differences in baseline MTH and isometric strength were observed between the sessions. MTH of the quadriceps and triceps surae increased (p < 0.05) during and immediately after the BFR-slow (8 to 11% and 2 to 4%, respectively) and BFR-fast (7 to 8% and 3 to 5%, respectively) sessions, but not in the CON-slow (-2% and 0%, respectively) session. There were no significant differences in quadriceps and triceps surae MTH between the BFR-slow and the BFR-fast sessions. No changes in MTH were observed for the lumbar multifidus following each walking session. Isometric strength was unchanged during and immediately after the BFR-slow, BFR-fast, and CON-slow sessions. Our results indicated that acute increases in muscle size occurs following walk exercise combined with leg blood flow restriction regardless of gait speed which may influence BFR-walk induced muscle hypertrophy. Key words: Vascular occlusion, ultrasonography, muscle size, maximum voluntary contraction.

Sarcolemmal permeability and muscle damage as hypertrophic stimuli in blood flow restricted resistance exercise (Reply to Loenneke and Abe)

Dear Editor,We welcome the letter by Loenneke and Abe (2011)relating to our recent publication (Wernbom et al. 2011), aswe feel that the topics are of importance and deserve fur-ther discussion.1. Regarding their first point, we were interested instudying the recovery of maximal voluntary contraction(MVC) during maintained partial blood flow restriction(BFR) in order to document the acute effects of our BFRmodel on muscle function during and after exercise, whileblood flow was still restricted. We were also aiming tostudy later recovery, hence our choice of time points.2. Regarding their second point, we acknowledge thatthere were no significant differences in MVC after the BFRwas released. However, there was a trend for MVC of theBFR leg to still be reduced at 72 h post-exercise(p\0.10), the nonsignificance possibly reflecting a type IIerror. Nevertheless, some signs of membrane permeabilitywere present also in the free-flow leg, see below.Concerning signs of damage in the BFR leg, Umbelet al. (2009) demonstrated greater reductions in MVC(-14.1 vs. -1.5%) in the BFR leg than in the free-flowtrained leg at 24 h post-exercise. Interestingly, inspectionof their figures on vastus lateralis cross-sectional area(CSA) reveals a muscle swelling of *5.5% at 24 h post-exercise (vs. *2% in the free-flow leg), and the swelling at24 h was significant when the CSA data for both legs werecombined. The moderate torque decrements, muscleswelling and delayed onset muscle soreness (DOMS) areconsistent with the suggestion of mild muscle damage, asproposed by Umbel et al. (2009). The torque decrements,the signs of increased membrane permeability, the pro-longed increase in resting tension, and DOMS in our study(Wernbom et al. 2011) are also consistent with thisproposal.There are other reports that signs of muscle damage canbe induced by low-to-moderate load resistance exerciseduring ischemic conditions (see point 3), and also a casereport on rhabdomyolysis after BFR-resistance exercise(Iversen and Rostad 2010). These findings suggest that thepotential for muscle damage with strenuous acute BFR-resistance exercise needs to be taken seriously.However, it should also be emphasised that this was thefirst time that our subjects performed strenuous BFR-resistance exercise. It is our experience that the symptomsof muscle damage are much less evident with subsequentbouts, suggesting a protective ‘‘repeated-bout effect’’similar to that for eccentric exercise.3. Concerning Loenneke and Abe’s third point, it shouldbe noted that the exercise was performed without relaxa-tion between repetitions. Signs of ischemia with continuousdynamic knee-extensions have been noted at loads as lowas 10% of MVC (Shoemaker et al. 1994), and isometricknee-extensions at 25–35% of MVC elicited a similar

Does blood flow restricted exercise result in prolonged torque decrements and muscle damage?

We are writing in regard to the recent paper from Wernbom et al. (2011) titled ‘‘Contractile function and sarcolemmal permeability after acute low-load resistance exercise with blood flow restriction.’’ The authors sought to investigate neuromuscular fatigue and recovery, as well as fiber morphology, following an acute bout of low-load resistance exercise with blood flow restriction (BFR). The authors should be commended on investigating the effects of BFR at the muscle fiber level, as this is an area that is presently poorly considered in the current literature. The authors hypothesized that exercise with BFR would result in signs of muscle damage. However, we have some concerns with the interpretation of the data presented in this study. Several of the authors’ main findings, highlighted in the discussion, may not necessarily be attributed to muscle damage. The authors’ first main finding was that there were markedly larger acute reductions (1 and 2 min postexercise) in maximum voluntary contraction (MVC) in the BFR leg compared to the free-flow leg. It should be emphasized that these greater acute reductions observed in the BFR leg were obtained with a MVC completed under BFR. Following the release of the cuff, there were no longer differences between groups. Furthermore, we question the reasoning behind having subjects’ complete repetitions to muscular failure under BFR, followed by two MVC’s which were also completed under BFR. If the purpose was to investigate the effects of low-load BFR on muscle damage, it seems more appropriate to release the cuff following the completion of the exercise bout for at least one of the immediate post MVC’s. This marked decrease in MVC can be questioned, because previous research has shown that decreases observed in MVC with BFR are almost returned to baseline within a minute following the release of the cuff (Yasuda et al. 2009). The authors second main finding was that part of the decline in MVC was longer lasting (at least 48 h), especially in the BFR leg. Again, the MVC’s which were different between conditions, were only observed when the MVC was completed under BFR. The authors’ suggestion that the decline in MVC was longer lasting is not supported by the data presented in the paper, which showed that there were no differences between groups at 4, 24, or 48 h postexercise. The authors’ third main finding was that there was an increased occurrence of fibers with elevated tetranectin staining in the BFR leg. The authors suggest this elevated tetranectin staining is indicative of muscle damage, because unpublished data from their laboratory suggest that severe eccentric exercise caused marked increases with intracellular tetranectin staining. While this is interesting, it should be noted that the exercise completed in this study was submaximal and not severe eccentric exercise. Furthermore, elevations in tetranectin staining were also observed in the free-flow leg which was not taken to muscular failure (work matched with BFR leg), indicating that the elevation in tetranectin may not have been reflective of muscle damage. The authors did state that tetranectin elevations are not necessarily only associated with muscle damage, but may also contribute to mechanotransduction processes, which may be of mechanistic importance for the explanation of the muscle hypertrophy Communicated by Susan A. Ward.

Contractile function and sarcolemmal permeability after acute low-load resistance exercise with blood flow restriction

Conflicting findings have been reported regarding muscle damage with low-intensity resistance exercise with blood flow restriction (BFR) by pressure cuffs. This study investigated muscle function and muscle fibre morphology after a single bout of low-intensity resistance exercise with and without BFR. Twelve physically active subjects performed unilateral knee extensions at 30% of their one repetition maximum (1RM), with partial BFR on one leg and the other leg without occlusion. With the BFR leg, five sets were performed to concentric torque failure, and the free-flow leg repeated the exact same number of repetitions and sets. Biopsies were obtained from vastus lateralis before and 1, 24 and 48 h after exercise. Maximum isometric torque (MVC) and resting tension were measured before and after exercise and at 4, 24, 48, 72, 96 and 168 h post-exercise. The results demonstrated significant decrements in MVC (lasting ≥48 h) and delayed onset muscle soreness in both legs, and increased resting tension for the occluded leg both acutely and at 24 h post-exercise. The percentage of muscle fibres showing elevated intracellular staining of the plasma protein tetranectin, a marker for sarcolemmal permeability, was significantly increased from 9% before exercise to 27-38% at 1, 24 and 48 h post-exercise for the BFR leg. The changes in the free-flow leg were significant only at 24 h (19%). We conclude that an acute bout of low-load resistance exercise with BFR resulted in changes suggesting muscle damage, which may have implications both for safety aspects and for the training stimulus with BFR exercise.

Effects of Leg Blood Flow Restriction during Walking on Cardiovascular Function

Exercise with limb blood flow restriction (BFR) is a very popular exercise modality in Japan and is spreading widely to the rest of the world. The underlying principle of this training modality is that under the conditions of restricted blood flow, even low-intensity exercise can provide significant muscle strength and hypertrophy. One concern, however, is that BFR during exercise may place unnecessary burden on those with compromised cardiac function. We determined the impact of leg BFR during walking on cardiovascular function in 17 young (26 ± 1 yr) healthy volunteers. Each subject underwent five bouts of 2-min treadmill walking at 2 miles·h(-1) with 1-min interval either with or without tourniquet cuffs inflated on both thighs. Heart rate increased more during the BFR session, whereas stroke volume decreased greater during the BFR session. Blood pressure increased significantly and substantially during the BFR session. Consequently, an increase in double product, an index of myocardial oxygen demand, was more than threefold higher in the BFR condition. Systemic arterial compliance evaluated by stroke volume/pulse pressure ratio significantly increased during the control session by 14% but reduced during the BFR condition by 19%. Popliteal artery flow-mediated vasodilation decreased significantly after the exercise with BFR but not after the control session. Even at low intensity, the aerobic exercise with BFR requires a greater cardiac work and decreases endothelial function. Limb BFR during exercise may need to be more cautiously prescribed to those with compromised cardiac conditions.