Low-load Blood Flow Restricted Exercise Research Articles

Acute hypoalgesic, neurophysiological and perceptual responses to low-load blood flow restriction exercise and high-load resistance exercise.

This study compared the acute hypoalgesic and neurophysiological responses to low-load resistance exercise with and without blood flow restriction (BFR), and free-flow, high-load exercise. Participants performed four experimental conditions where they completed baseline measures of pain pressure threshold (PPT), maximum voluntary force (MVF) with peripheral nerve stimulation to determine central and peripheral fatigue. Corticospinal excitability (CSE), corticospinal inhibition and short interval intracortical inhibition (SICI) were estimated with transcranial magnetic stimulation. Participants then performed low-load leg press exercise at 30% of one-repetition maximum (LL); low-load leg press with BFR at 40% (BFR40) or 80% (BFR80) of limb occlusion pressure; or high-load leg press of four sets of 10 repetitions at 70% one-repetition maximum (HL). Measurements were repeated at 5, 45min and 24h post-exercise. There were no differences in CSE or SICI between conditions (all P>0.05); however, corticospinal inhibition was reduced to a greater extent (11%-14%) in all low-load conditions compared to HL (P<0.005). PPTs were 12%-16% greater at 5min post-exercise in BFR40, BFR80 and HL compared to LL (P≤0.016). Neuromuscular fatigue displayed no clear difference in the magnitude or time course between conditions (all P>0.05). In summary, low-load BFR resistance exercise does not induce different acute neurophysiological responses to low-load, free-flow exercise but it does promote a greater degree of hypoalgesia and reduces corticospinal inhibition more than high-load exercise, making it a useful rehabilitation tool. The changes in neurophysiology following exercise were not related to changes in PPT.

Changes in the QTc Interval Following High-Load and Low-Load Blood Flow Restriction Exercise

Changes in the QTc Interval Following High-Load and Low-Load Blood Flow Restriction Exercise

Low-Load Blood-Flow Restriction Exercise to Failure and Nonfailure and Myoelectric Activity: A Meta-Analysis.

To compare the short- and long-term effects of low-load resistance training with blood-flow restriction (LL-BFR) versus low- (LL-RT) or high- (HL-RT) load resistance training with free blood flow on myoelectric activity and investigate the differences between failure (exercise performed to volitional failure) and nonfailure (exercise not performed to volitional failure) protocols. We identified sources by searching the MEDLINE, PubMed, CINAHL, Web of Science, CENTRAL, Scopus, SPORTDiscus, and PEDro electronic databases. We screened the titles and abstracts of 1048 articles using our inclusion criteria. A total of 39 articles were selected for further analysis. Two reviewers independently assessed the methodologic quality of each study and extracted the data. A meta-analytic approach was used to compute standardized mean differences (SMDs) ± 95% CIs. Subgroup analyses were conducted for both failure and nonfailure protocols. The search identified 39 articles that met the inclusion criteria. Regarding the short-term effects, LL-BFR increased muscle excitability compared with LL-RT during nonfailure protocols (SMD = 0.61; 95% CI = 0.34, 0.88), whereas HL-RT increased muscle excitability compared with LL-BFR during failure (SMD = -0.61; 95% CI = -1.01, -0.21) and nonfailure (SMD = -1.13; 95% CI = -1.94, -0.33) protocols. Concerning the long-term effects, LL-BFR increased muscle excitability compared with LL-RT during exercises performed to failure (SMD = 1.09; 95% CI = 0.39, 1.79). Greater short-term muscle excitability levels were observed in LL-BFR than in LL-RT during nonfailure protocols. Conversely, greater muscle excitability was present during HL-RT than LL-BFR, regardless of volitional failure. Furthermore, LL-BFR performed to failure increased muscle excitability in the long term compared with LL-RT.

Muscle Swelling Following Low Load Blood Flow Restriction Exercise Does Not Differ Between Cuff Widths In The Lower Body

Acute muscle swelling is a purported mechanism for muscle hypertrophy following blood flow restriction (BFR) training. Currently there are numerous cuff widths used within the lower body BFR literature. However, studies suggest that growth may be attenuated with a wider cuff. Whether this is related to a differential acute swelling response has not been previously shown. PURPOSE: To examine the acute changes in muscle swelling following low load BFR exercise in the lower body, in response to different cuff widths inflated to the same relative pressure. METHODS: Ninety-six (43 men, 53 women) participants completed two conditions (one each leg). Participants completed four sets of unilateral knee extension exercise to failure using 30% of their one repetition maximum (1RM) with BFR applied with either a narrow (5 cm) or a wide (12 cm) cuff inflated to 40% of their arterial occlusion pressure. Muscle thickness and echo intensity were measured at two sites (proximal and distal) before and after each exercise bout as surrogate markers of swelling. A repeated measures analysis with a between subject factor of sex was used to assess changes. Bayes Factors (BF10) were used to quantify evidence. RESULTS: The difference in acute changes in muscle thickness (BF10: 0.43) and echo intensity (BF10: 0.87) between cuff widths was not different between the proximal (i.e. wide cuff covered this site) and distal (no cuff was over this site) location. Further, changes in muscle thickness at the proximal [5cm: 0.58 cm vs. 12 cm: 0.57 cm; median difference (95% credible interval) of 0.009 (-0.04, 0.06) cm] and distal [5 cm: 0.63 cm vs. 12 cm: 0.63 cm; median difference (95% credible interval) of 0.00002 (-0.03, 0.04) cm] site did not differ based on cuff width or sex (Men: 0.58 cm vs. Women: 0.57 cm and Men: 0.64 cm vs. Women: 0.63 cm for proximal and distal sites, respectively). Echo intensity appeared to decrease at the proximal and distal sites with no differences between cuff widths. However, there was some evidence that this change at the distal site may be different between sexes [BF10: 49.8; Men: -1.9 vs. Women: -4.2 AU). CONCLUSIONS: Acute muscle swelling occurs in men and women, even when using a wider cuff. Thus, if there is to be attenuation in growth with a wider cuff, it is unlikely to be due to differences in acute swelling.

Acute Muscular Responses to Practical Low-Load Blood Flow Restriction Exercise Versus Traditional Low-Load Blood Flow Restriction and High-/Low-Load Exercise.

Blood flow restriction (BFR) increases muscle size and strength when combined with low loads, but various methods are used to produce this stimulus. It is unclear how using elastic knee wraps can impact acute muscular responses compared with using nylon cuffs, where the pressure can be standardized. Investigate how elastic knee wraps compare with nylon cuffs and high-load (HL)/low-load (LL) resistance exercise. A randomized cross-over experimental design using 6 conditions combined with unilateral knee extension. Human Performance Laboratory. A total of 9 healthy participants (males = 7 and females = 2) and had an average age of 22 (4) years. LL (30% of 1-repetition maximum [1-RM]), HL (70% 1-RM), BFR at 40% of arterial occlusion pressure (BFR-LOW), BFR at 80% of arterial occlusion pressure (BFR-HIGH), elastic knee wraps stretched by 2 in (PRACTICAL-LOW), and elastic knee wraps stretched to a new length equivalent to 85% of thigh circumference (PRACTICAL-HIGH). BFR and practical conditions used 30% 1-RM. Muscle thickness, maximum voluntary isometric contraction, and electromyography amplitude. Bayesian statistics evaluated differences in changes between conditions using the Bayes factor (BF10), and median and 95% credible intervals were reported from the posterior distribution. Total repetitions completed were greater for BFR-LOW versus PRACTICAL-HIGH (BF10 = 3.2, 48.6 vs 44 repetitions) and greater for PRACTICAL-LOW versus BFR-HIGH (BF10 = 717, 51.8 vs 36.3 repetitions). Greater decreases in changes in maximum voluntary isometric contraction were found in PRACTICAL-HIGH versus HL (BF10 = 1035, ∼103N) and LL (BF10 = 45, ∼66N). No differences in changes in muscle thickness were found between LL versus PRACTICAL-LOW/PRACTICAL-HIGH conditions (BF10 = 0.32). Greater changes in electromyography amplitude were also found for BFR-LOW versus PRACTICAL-HIGH condition (BF10 = 6.13, ∼12%), but no differences were noted between the other BFR conditions. Overall, elastic knee wraps produce a more fatiguing stimulus than LL or HL conditions and might be used as an alternative to pneumatic cuffs that are traditionally used for BFR exercise.

The immune system in sporadic inclusion body myositis patients is not compromised by blood-flow restricted exercise training

BackgroundSporadic inclusion body myositis (sIBM) is clinically characterised by progressive proximal and distal muscle weakness and impaired physical function while skeletal muscle tissue displays abnormal cellular infiltration of T cells, macrophages, and dendritic cells. Only limited knowledge exists about the effects of low-load blood flow restriction exercise in sIBM patients, and its effect on the immunological responses at the myocellular level remains unknown. The present study is the first to investigate the longitudinal effects of low-load blood flow restriction exercise on innate and adaptive immune markers in skeletal muscle from sIBM patients.MethodsTwenty-two biopsy-validated sIBM patients were randomised into either 12 weeks of low-load blood flow restriction exercise (BFRE) or no exercise (CON). Five patients from the control group completed 12 weeks of BFRE immediately following participation in the 12-week control period leading to an intervention group of 16 patients. Muscle biopsies were obtained from either the m. tibialis anterior or the m. vastus lateralis for evaluation of CD3-, CD8-, CD68-, CD206-, CD244- and FOXP3-positive cells by three-colour immunofluorescence microscopy and Visiopharm-based image analysis quantification. A linear mixed model was used for the statistical analysis.ResultsMyocellular infiltration of CD3−/CD8+ expressing natural killer cells increased following BFRE (P < 0.05) with no changes in CON. No changes were observed for CD3+/CD8− or CD3+/CD8+ T cells in BFRE or CON. CD3+/CD244+ T cells decreased in CON, while no changes were observed in BFRE. Pronounced infiltration of M1 pro-inflammatory (CD68+/CD206−) and M2 anti-inflammatory (CD68+/CD206+) macrophages were observed at baseline; however, no longitudinal changes in macrophage content were observed for both groups.ConclusionsLow-load blood flow restriction exercise elicited an upregulation in CD3−/CD8+ expressing natural killer cell content, which suggests that 12 weeks of BFRE training evokes an amplified immune response in sIBM muscle. However, the observation of no changes in macrophage or T cell infiltration in the BFRE-trained patients indicates that patients with sIBM may engage in this type of exercise with no risk of intensified inflammatory activity.

Blood Flow-restricted Exercise Does Not Induce a Cross-Transfer of Effect: A Randomized Controlled Trial.

The goal of this trial was to determine whether low-load blood flow-restricted (BFR) exercise of appendicular muscles induces a cross-transfer of effect to the trunk extensor (TE) muscles, such that low-load TE exercise would enhance TE size and function to a greater extent than standard low-load exercise in people with recurrent low back pain (LBP). We also investigated the direct effects of BFR exercise in the appendicular muscles. Thirty-two adults with recurrent, nonspecific LBP were randomized into two groups: Appendicular BFR exercise (BFR exercise) or control exercise (CON exercise). All participants trained (two times per week) for 10 wk, with a 12-wk follow-up. Participants performed three sets of leg extension (LE), plantar flexion (PF), and elbow flexion (EF) exercises followed by low-load TE exercise without BFR. Outcome measures included magnetic resonance imaging-derived muscle size (quadriceps and TE), strength (LE, PF, EF, and TE), and endurance (LE and TE). There was no evidence for a cross-transfer of effect to the TE. There was also no statistically significant enhancement of limb skeletal muscle size or function of BFR relative to CON exercise at any time point; though, moderate effect sizes for BFR exercise were observed for enhanced muscle size and strength in the leg extensors. Low-load BFR exercise of the appendicular muscles did not result in a cross-transfer of effect to the TE musculature. There was also no significant benefit of low-load BFR exercise on the appendicular muscle size and function, suggesting no benefit from low-load BFR exercise in adults with recurrent, nonspecific LBP.

Hemodynamic Responses to Low-Load Blood Flow Restriction and Unrestricted High-Load Resistance Exercise in Older Women.

Introduction: Blood flow restriction (BFR) during low-load resistance exercise increases muscle size similarly to high-load training, and may be an alternative to lifting heavy weights for older people at risk of sarcopenia. However, few studies have addressed the safety of such exercise in older people, or whether this is impacted by the actual exercises performed during training. This study aimed to compare the acute hemodynamic and perceptual responses during low-load BFR exercise to unrestricted low-load and high-load exercise in older women, and to determine whether these responses depend on the type of exercise performed.Methods: Fifteen older women (63–75 year) were assessed for maximal strength (1RM) in the leg press and leg extension. Participants then completed three protocols using these exercises in a randomized order: (1) low-load exercise (LL); (2) low-load exercise with BFR (LLBFR), and; (3) high-load exercise (HL). Blood pressure was assessed at baseline and after each set, and impedance cardiography measured cardiovascular function during trials. Rating of perceived exertion (RPE) and muscle soreness scores were obtained throughout trials.Results: Baseline hemodynamic values were consistent between trials. Systolic, diastolic, and mean arterial pressures were higher in LLBFR compared with HL and LL (p ≤ 0.021). The LL condition resulted in lower heart rate (p ≤ 0.002) and rate-pressure product (p ≤ 0.011) responses compared with LLBFR and HL. The leg press generally conferred greater hemodynamic and perceptual demands than the leg extension for all conditions (p ≤ 0.002). RPE was lower during LL compared with LLBFR and HL (p ≤ 0.008), and there were no between-condition differences in perceived muscle soreness.Conclusion: The blood pressure data indicate that LLBFR causes greater stress on the vasculature than LL and HL exercise, and that the leg press was generally more demanding than the leg extension. While additional cardiovascular measures were similar between LLBFR and HL conditions, caution should be advised when prescribing BFR exercise for individuals with compromised cardiac or vascular function. Nevertheless, LLBFR and HL exercise were perceived similarly, indicating that BFR training may be viable for healthy older people.

Short-Term Preconditioning With Blood Flow Restricted Exercise Preserves Quadriceps Muscle Endurance in Patients After Anterior Cruciate Ligament Reconstruction.

Surgical ACL reconstruction performed with a tourniquet induces compression and ischemic stress of the quadriceps femoris (QF) muscle which can accelerate postoperative weakness. Given that low-load blood flow restricted (BFR) exercise is potent in enhancing muscle oxygenation and vascular function, we hypothesized that short-term preconditioning with low-load BFR exercise can attenuate QF muscle endurance deterioration in the postoperative period. Twenty subjects undergoing arthroscopic ACL reconstruction performed 5 exercise sessions in the last 8 days prior to surgery. They were assigned into either BFR group, performing low-load BFR knee-extension exercise, or SHAM-BFR group, replicating equal training volume with sham occlusion. Blood flow (near-infrared spectroscopy) and surface EMG of QF muscle during sustained isometric contraction at 30% of maximal voluntary isometric contraction (MVIC) torque performed to volitional failure were measured prior to the intervention and again 4 and 12 weeks after surgery. There was an overall decrease (p = 0.033) in MVIC torque over time, however, no significant time-group interaction was found. The time of sustained QF contraction shortened (p = 0.002) in SHAM-BFR group by 97 ± 85 s at week 4 and returned to preoperative values at week 12. No change in the time of sustained contraction was detected in BFR group at any time point after surgery. RMS EMG amplitude increased (p = 0.009) by 54 ± 58% at week 4 after surgery in BFR group only. BFm increased (p = 0.004) by 52 ± 47% in BFR group, and decreased (p = 0.023) by 32 ± 19% in SHAM-BFR group at week 4 after surgery. Multivariate regression models of postoperative changes in time of sustained QF contraction revealed its high correlation (R2 = 0.838; p < 0.001) with changes in BFm and RMS EMG in the SHAM-BFR group, whereas no such association was found in the BFR group. In conclusion, enhanced endurance of QF muscle was triggered by combination of augmented muscle fiber recruitment and enhanced muscle perfusion. The latter alludes to a preserving effect of preconditioning with BFR exercise on density and function of QF muscle microcirculation within the first 4 weeks after ACL reconstruction.

Multiple Strength Assessments to Evaluate Adaptations to High-Load and Low-Load Blood Flow Restricted Exercise

Differences in muscle strength adaptations between high-load (HL) and low-load blood flow restricted (BFR) resistance training protocols may be due to the type of strength test performed (e.g isotonic, isokinetic and isometric). PURPOSE: To assess differences in isotonic, isometric and isokinetic strength adaptations in older adults following HL and BFR resistance training. METHODS: Thirty-six males and females (mean: 75.6+7.6 years, 1.67+.09 m, 74.3+13.2 kg) classified as being at risk of mobility limitations were randomly assigned to HL (70% 1-RM) or low-load BFR (30% 1-RM coupled with a vascular restriction) exercise for the knee extensors twice per week for 6 weeks. A control group performed light upper body resistance and flexibility training. Knee extension 10-RM to predict 1-RM strength, isometric maximum voluntary contraction (MVC) and isokinetic strength at 60[BULLET OPERATOR]s-1, 180[BULLET OPERATOR]s-1, and 300[BULLET OPERATOR]s-1were measured before and after 6-weeks of training. RESULTS: HL and BFR training increased predicted 1-RM strength 34% (P<.001) and 24% (P<.001) respectively, from baseline to 6-weeks of training. HL training produced a 16% increase in MVC (P=.002) while BFR training did not change (P=.91). No interventions, included the control, resulted in changes in isokinetic strength at the various speeds (P>.20). CONCLUSION: Strength improvements from HL resistance training carried over to other strength tests. This favorable adaptation did not occur following BFR exercise which may limit the effectiveness of this training program. Isotonic training does not carry over to isokinetic strength adaptations and therefore may be a drawback when implementing resistance training programs for older adults. Supported by NIH grant 1R15 A6040700-01A1.

Effects of low-load resistance exercise with blood flow restriction on high-energy phosphate metabolism and oxygenation level in skeletal muscle

We aimed to evaluate the effects of low-load resistance exercise with blood flow restriction (BFR) on high-energy phosphate metabolism, intracellular pH, and oxygenation level in the skeletal muscle. Seven males performed low-load ankle plantar flexion exercise (120 repetitions, 30% of one-repetition maximum) with and without BFR (130% of systolic blood pressure) inside a magnetic resonance device. Inorganic phosphate (Pi)-to-phosphocreatine (PCr) ratio, intracellular pH, and tissue oxygenation index (TOI) in the medial gastrocnemius were determined using 31P-magnetic resonance spectroscopy and near-infrared spectroscopy before and during exercise. The Pi-to-PCr ratio significantly increased during exercise in both conditions, with the BFR-condition values significantly exceeding the control-condition values. The BFR and control conditions showed significantly decreased intracellular pH during exercise, with the BFR-condition values being significantly lower than the control-condition values. The TOI significantly decreased during both exercises, but the decreases in the BFR condition were significantly greater than those observed in the control condition. Low-load BFR exercise places greater metabolic stress (greater PCr depletion, lower intracellular pH, and lower oxygenation level) on an exercising muscle than low-load non-restricted exercise.

Cardiovascular And Perceptual Responses To Various Blood Flow Restriction Pressures And Exercise Loads

Blood flow restriction (BFR) allows individuals to exercise with lower loads while producing similar increases in muscle size as high load training. Most studies implement moderate to high pressures with loads corresponding to 20-30% of their one-repetition maximum (1RM). No study has examined perceptual or cardiovascular responses using loads lower than 20% 1RM, which may provide a more widely inclusive and palatable stimulus. PURPOSE: To determine the cardiovascular and perceptual response to very low load BFR exercise using both moderate (40%) and high (80%) relative arterial occlusion pressures (AOP). METHODS: 14 participants came to the lab on four separate days to complete six exercise protocols (2 per visit on visits 2-4) consisting of 4 sets (1 set of 30 followed by 3 sets of 15) of BFR elbow flexion exercise with either a 10%, 15% or 20% 1RM load, each of which was performed with a moderate (40% AOP) and high (80% AOP) relative pressure. A repeated measures ANOVA was used to determine differences in AOP pre and post exercise and a Friedman test was used to determine differences in discomfort and ratings of perceived exertion (RPE) following each set. AOP is expressed as [mean (95% confidence interval)] with RPE and discomfort expressed as [median (25th, 75th percentile)]. RESULTS: There was an interaction for AOP (p=0.002) with higher pressures and loads producing a gradient increase. The pre to post changes ranged from 21 (95% CI: 10-32) mmHg in the 10% 1RM/40% AOP condition to 62 (95% CI: 45-78) mmHg in the 20% 1RM/80% AOP condition. Ratings of discomfort were primarily dependent on the level of restriction pressure applied, with higher pressures resulting in greater discomfort (p<0.001) ranging from 2.5 (1, 5) in the 15% 1RM/40% AOP condition to 6.5 (5.5, 7.25) in the 15% 1RM/80% AOP condition. Additionally, a gradient increase in RPE accompanied higher pressures and loads which ranged from 8.5 (7,12) at the conclusion of the 10%1RM/40% AOP condition to 15.5 (12.75, 17.25) at the conclusion of the 20% 1RM/80% AOP condition. CONCLUSIONS: Increases in load and restrictive pressure resulted in elevated AOP and RPE, but higher pressures were primarily responsible for increased discomfort. Individuals experiencing discomfort during low load BFR exercise may wish to decrease the applied pressure and increase the exercise load.

The Effect of Cuff Width on Muscle Adaptations after Blood Flow Restriction Training.

Blood flow restriction in combination with low-load resistance training has been shown to increase muscle size and strength; however, the influence of cuff width on these adaptations is unknown. The objective of this study is to determine the influence of different cuff widths on muscle size and strength, and also investigate whether a wider cuff would result in less adaptation compared with a narrow cuff when inflated to the same relative pressure (80% arterial occlusion pressure). Eleven physically active males had their arms randomly divided into two separate conditions: low-load blood flow restriction exercise with a narrow cuff (BFR + N, 5 cm) and low-load blood flow restriction exercise with a wide cuff (BFR + W, 10 cm). All participants underwent 12 wk of unilateral elbow flexion at 20% of their one-repetition maximum (1RM). The elbow flexion strength (1RM), elbow flexor muscle cross-sectional area (CSA), arterial blood flow, training volume, RPE, and rating of perceived pain were assessed before and after training. Elbow flexion 1RM and CSA significantly increased in both conditions (BFR + N = 13.5% and 9% vs BFR + W = 11.9% and 11.2%, respectively). The arterial blood flow was significantly reduced when 80% of the arterial occlusion pressure was applied in both conditions (BFR + N = 61.2% and BFR + W = 63.5%). There were no significant differences in the training volume, RPE, or rating of perceived pain between conditions (P > 0.05). We wish to suggest that, regardless of cuff width, both protocols produced similar increases in 1RM and elbow flexor muscle CSA, and these responses may be related to the similar training volume and/or similar reductions in arterial blood flow produced when both cuffs were inflated to the same relative pressure.

The Influence Of Cuff Width On Regional Muscle Growth

A variety of protocols with different cuff widths have been used with blood flow restriction training (BFR). However, little is known about the influence of cuff width on muscle adaptations. PURPOSE: To determine if the cuff width differentially affects regional muscle growth and strength with BFR. METHODS: Eleven active males (mean ± SD: age 25.2 ± 6.1 years, height 1.70 ± 0.1 m, body mass 74.9 ± 9.5 kg) volunteered for the study. Subjects had their legs randomly divided into two conditions: low-load blood flow restriction exercise with a narrow cuff (NBFR - 7 cm) and low-load blood flow restriction exercise with a wide cuff (WBFR - 17.5 cm). Both cuffs were placed on the proximal portion of the thigh and inflated to 80% of the resting arterial occlusion pressure for each cuff. All subjects performed unilateral knee extension 2x/week, 3 sets to volitional failure, 60s rest interval, at 20% 1RM, for 12 weeks. The cuffs remained inflated throughout each exercise session and deflated at the end of exercise. Knee extension strength (1RM), cross-sectional area (CSA) of different quadriceps regions (proximal, middle and distal), exercise volume and femoral blood flow were assessed for both cuff sizes. A repeated measures ANOVA was performed for each dependent variable, and statistical significance was set at p≤ 0.05. RESULTS: Knee extension 1RM increased in both conditions (NBFR=6% vs WBFR=9.5%, p<0.001). The CSA of the proximal region did not change following either condition (p>0.05), however, more than half of subjects from WBFR had their CSA reduced. There were increases in CSA of the middle and distal regions in the NBFR (6.2% and 5.6%) and WBFR (3% and 5.4%), respectively. The NBFR condition completed greater exercise volume compared to the WBFR (1026 kg vs 750 kg). The femoral blood flow was similarly reduced in both conditions (NBFR = 58.1% vs WBFR = 70%). CONCLUSIONS: There were no changes in skeletal muscle CSA of the proximal region with either the wide or narrow cuff. Further, and although not significant, individual response data suggested that the proximal and middle regions may have also been attenuated and/or reduced by the wide cuff in some participants. These preliminary findings appear to suggest that cuff width may exert differential responses despite being inflated to the same relative pressure.

Nutrition coupled with high-load or low-load blood flow restricted exercise during human limb suspension

Background High-load resistance exercise (HRE) and low-load blood flow restricted (BFR) exercise have demonstrated efficacy for attenuating unloading related muscle atrophy and dysfunction. Protein consumption immediately before and/or after exercise has been shown to increase the skeletal muscle anabolic response to resistance training. The purpose of this study was to compare the skeletal muscle adaptations when chocolate milk intake was coupled with HRE or low-load BFR exercise during simulated lower limb weightlessness.

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.

Myogenic and proteolytic mRNA expression following blood flow restricted exercise

Resistance exercise performed at low loads (20-30% of maximal strength) with blood flow restriction (BFR) acutely increases protein synthesis and induces hypertrophy when performed chronically. We investigated myogenic and proteolytic mRNA expression 8 h following an acute bout of knee extension exercise. Fifteen subjects (22.8 ± 3.7 years, eight men and seven women) were randomized to two exercise conditions: BFR or control exercise. All participants performed four sets of exercise (30, 15, 15 and 15 repetitions) at 20% of maximal strength. Persons in the BFR group had a cuff placed on the upper thigh inflated to 1.5 times brachial systolic blood pressure (cuff pressure range: 135-186 mmHg). Muscle biopsies from the vastus lateralis were excised 24 h before and 8 h following the exercise. RT-PCR analysis demonstrated no change in myogenic gene expression (insulin-like growth factor-1, MyoD, myogenin, myostatin - a negative regulator) with either exercise condition (P > 0.123). However, BFR exercise downregulated mRNA expression in transcripts associated with proteolytic pathways (FOXO3A, Atrogin-1 and MuRF-1) with no change in the control exercise condition. Specifically, median mRNA expression of FOXO3A decreased by 1.92-fold (P = 0.01), Atrogin-1 by 2.10-fold (P = 0.01) and MuRF-1 by 2.44-fold (P = 0.01). These data are consistent with the downregulation of proteolytic transcripts observed following high-load resistance exercise. In summary, myogenic genes are unchanged and proteolytic genes associated with muscle remodelling are reduced 8 h following low-load BFR exercise.

Delayed-onset muscle soreness induced by low-load blood flow-restricted exercise

We performed two experiments to describe the magnitude of delayed-onset muscle soreness (DOMS) associated with blood flow restriction (BFR) exercise and to determine the contribution of the concentric (CON) versus eccentric (ECC) actions of BFR exercise on DOMS. In experiment 1, nine subjects performed three sets of unilateral knee extension BFR exercise at 35% of maximal voluntary contraction (MVC) to failure with a thigh cuff inflated 30% above brachial systolic pressure. Subjects repeated the protocol with the contralateral limb without flow restriction. Resting soreness (0-10 scale) and algometry (pain-pressure threshold; PPT) were assessed before and 24, 48 and 96 h post-exercise. Additionally, MVC and vastus lateralis cross-sectional area (CSA) were measured as indices of exercise-induced muscle damage. At 24-h post-exercise, BFR exercise resulted in more soreness than exercise without BFR (2.8 +/- 0.3 vs 1.7 +/- 0.5) and greater reductions in PPT (15.2 +/- 1.7 vs. 20 +/- 2.3 N) and MVC (14.1 +/- 2.5% decrease vs. 1.5 +/- 4.5% decrease) (p <or= 0.05). In experiment 2, 15 different subjects performed three sets of unilateral BFR exercise at 35% MVC with one limb performing only the CON action and the contralateral performing the ECC action. The aforementioned indices of DOMS were assessed before exercise and 24, 48 and 96 h post-exercise. At 24 h post-exercise, CON BFR exercise resulted in more resting soreness than ECC BFR exercise (3.0 +/- 0.5 vs. 1.6 +/- 0.4), and a greater decrease in MVC (9.8 +/- 2.7% decrease vs. 3.4 +/- 2.5% decrease) (p <or= 0.05). These data suggest that knee extension BFR exercise induces mild DOMS and that BFR exercise elicits muscle damage under atypical conditions with low-tension concentric contractions.