Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans

Neuromuscular effects of dorsiflexor training with and without blood flow restriction

Blood flow restriction training (BFRT) has been proposed for elderly and clinical populations with weakness. Before being used in these populations it is important to understand the neurological effects of, and subject perceptions to, BFRT. Seventeen healthy subjects were recruited and performed 2 experimental sessions, BFRT and training without blood flow restriction (TR-only), on separate days. Four sets of concentric/eccentric dorsiflexion contractions against theraband resistance were performed. Surface electromyography of the tibialis anterior was recorded during exercise and for the electrophysiological measures. At baseline, immediately-post, 10-min-post and 20-min-post exercise, motor evoked potentials (MEPs) from single pulse transcranial magnetic stimulation (TMS), paired-pulse TMS with interstimulus intervals of 2-ms (SICI) and 15-ms (ICF), and the M-max amplitude were recorded in the resting TA. Following training, subjects provided a numerical rating of the levels of pain, discomfort, fatigue, focus and difficulty during training. Muscle activation was higher in the last 20 contractions during BFRT compared to TR. There was no difference (time × condition interaction) between BFRT and TR for single-pulse MEP, SICI, ICF or M-max amplitude. There was a significant main effect of timepoint for single-pulse MEP and M-max amplitudes with both significantly reduced for 20-min-post exercise. No reductions were observed for SICI and ICF amplitudes. Taken together, BFRT and TR-only were only different during exercise and both regimes induced similar significant reductions in M-Max and MEP-amplitude post-training. Due to the lack of changes in SICI and ICF, it is unlikely that changes occurred in cortical sites related to these pathways. The increased surface electromyography activity in the last 20 contractions, indicate that the training regimes are different and that BFRT possibly induces more fatigue than TR. As such, BFRT could be used as an adjunct to conventional training. However, as subjects perceived BFRT as more painful, difficult and uncomfortable than TR-only, people should be selected carefully to undertake BFRT.

Eccentric and concentric blood flow restriction resistance training on indices of delayed onset muscle soreness in untrained women

PURPOSE

Unaccustomed exercise can result in delayed onset muscle soreness (DOMS), particularly as a result of the eccentric phase of the muscle contraction. Resistance training combined with venous blood flow restriction (vBFR) may attenuate DOMS, but the available information in this regard is conflicting. Therefore, the purpose of this study was to examine the effects of low-load eccentric vBFR (Ecc-vBFR) and concentric vBFR (Con-vBFR) resistance training on indices of DOMS.

METHODS

Twenty-five previously untrained women completed seven days of either Ecc-vBFR (n = 12) or Con-vBFR (n = 13) forearm flexion resistance training at a velocity of 120° s^-1 on an isokinetic dynamometer. The Ecc-vBFR group used a training load that corresponded to 30% of eccentric peak torque and the Con-vBFR group used a training load that corresponded to 30% of concentric peak torque.

RESULTS

There were no differences between Ecc-vBFR and Con-vBFR at any of the seven training sessions on any of the indices of DOMS. There were no decreases in the maximal voluntary isometric contraction torque which increased at days 6 and 7. Similarly, there were no changes in perceived muscle soreness, pain pressure threshold, elbow joint angle, or edema (as assessed by echo intensity via ultrasound) across the seven training sessions.

CONCLUSIONS

The Ecc-vBFR and Con-vBFR low-load training protocols were not associated with DOMS and there were no differences between protocols when performed using the same relative training intensity. These findings suggested that both unaccustomed eccentric and concentric low-load training did not result in DOMS when combined with vBFR.

The Effects of Restriction Pressures on the Acute Responses to Blood Flow Restriction Exercise

Purpose

No current guidelines or recommendations exist informing the selection of restriction pressure during blood flow restriction exercise (BFRE). Moreover, the effects of specific relative restriction pressures on the acute muscle, metabolic and cardiopulmonary responses to BFRE are unclear. The purpose of this study was to characterize these acute responses at different levels of restriction pressure.

Methods

Participants (n = 10) completed rhythmic isometric knee extension exercise across five experimental trials in a balanced randomized order. Three were BFRE trials {B-40 [restriction pressure set to 40% LOP (total limb occlusion pressure)]; B-60 (60% LOP); and B-80 (80% LOP)} with a workload equivalent to 20% maximal voluntary force (MVC), one was non-BFRE at 20% MVC (LL) and one was non-BFRE at 80% MVC (HL). Measurements recorded were torque, muscle activity via electromyography (EMG), tissue oxygenation via near infrared spectroscopy, whole body oxygen consumption, blood lactate and heart rate.

Results

For the LL and B-40 trials, most measures remained constant. However, for the B-60 and B-80 trials, significant fatigue was demonstrated by a reduction in MVC torque across the trial (p < 0.05). Blood lactate increased from baseline in HL, B-60, and B-80 (p < 0.05). Submaximal EMG was greater in B-60 and B-80 than LL, but lower compared with HL (p < 0.05). Tissue oxygenation decreased in HL, B-40, B-60, and B-80 (p < 0.05), which was lower in the B-80 trial compared to all other trials (p < 0.01). Whole body oxygen consumption was not different between the BFRE trials (p > 0.05).

Conclusion

We demonstrate graded/progressive acute responses with increasing applied pressure during BFRE, from which we speculate that an effective minimum “threshold” around 60% LOP may be necessary for BFRE to be effective with training. While these data provide some insight on the possible mechanisms by which BFRE develops skeletal muscle size and strength when undertaken chronically across a training program, the outcomes of chronic training programs using different levels of applied restriction pressures remain to be tested. Overall, the present study recommends 60–80% LOP as a suitable “minimum” BFRE pressure.

Blood Flow Restriction Increases the Neural Activation of the Knee Extensors During Very Low-Intensity Leg Extension Exercise in Cardiovascular Patients: A Pilot Study

Blood flow restriction (BFR) has the potential to augment muscle activation, which underlies strengthening and hypertrophic effects of exercise on skeletal muscle. We quantified the effects of BFR on muscle activation in the rectus femoris (RF), the vastus lateralis (VL), and the vastus medialis (VM) in concentric and eccentric contraction phases of low-intensity (10% and 20% of one repetition maximum) leg extension in seven cardiovascular patients who performed leg extension in four conditions: at 10% and 20% intensities with and without BFR. Each condition consisted of three sets of 30 trials with 30 s of rest between sets and 5 min of rest between conditions. Electromyographic activity (EMG) from RF, VL, and VM for 30 repetitions was divided into blocks of 10 trials and averaged for each block in each muscle. At 10% intensity, BFR increased EMG of all muscles across the three blocks in both concentric and eccentric contraction phases. At 20% intensity, EMG activity in response to BFR tended to not to increase further than what it was at 10% intensity. We concluded that very low 10% intensity exercise with BFR may maximize the benefits of BFR on muscle activation and minimize exercise burden on cardiovascular patients.

Strength training with blood flow restriction - a novel therapeutic approach for older adults with sarcopenia? A case report

Introduction

A 91-year-old sedentary man presenting exhaustion, lower-limb weakness, hypertension, and history of multiple falls was diagnosed with sarcopenia – appendicular skeletal muscle mass index (ASM) of 7.10 kg/m².

Purpose

To investigate the effects of strength training performed with low intensity in isolation (LI) or with blood flow restriction (LI-BFR) on strength, muscle mass, IGF-1, endothelial function, microcirculation, inflammatory biomarkers, and oxidative stress.

Methods

In the first 3 months, LI was performed with intensity corresponding to 30% of 1 repetition maximum, followed by 1 month of inactivity, and another 3 months of LI-BFR (similar load than LI concomitant to BFR equivalent to 50% of resting systolic blood pressure).

Results

LI-BFR, but not LI improved muscle mass, ASM, handgrip strength, isokinetic peak torque, IL-6, and IGF-1. Endothelial function, red blood cell velocity, and concentrations of C-reactive protein, and soluble intercellular adhesion molecules-1 improved after both LI and LI-BFR. Endothelin-1 and oxidative stress increased after LI-BFR, and lowered after LI.

Conclusion

LI-BFR, but not LI improved strength, muscle mass, IGF-1, endothelial function, and selected inflammatory markers in a nonagenarian sarcopenic patient. These results are promising and suggest that LI-BFR should be considered as an alternative to prevent muscle loss and improve functional fitness in frail older populations.

Effect of Blood Flow Restriction Training on Quadriceps Muscle Strength, Morphology, Physiology, and Knee Biomechanics Before and After Anterior Cruciate Ligament Reconstruction: Protocol for a Randomized Clinical Trial

BACKGROUND

Despite best practice, quadriceps strength deficits often persist for years after anterior cruciate ligament reconstruction. Blood flow restriction training (BFRT) is a possible new intervention that applies a pressurized cuff to the proximal thigh that partially occludes blood flow as the patient exercises, which enables patients to train at reduced loads. This training is believed to result in the same benefits as if the patients were training under high loads.

OBJECTIVE

The objective is to evaluate the effect of BFRT on quadriceps strength and knee biomechanics and to identify the potential mechanism(s) of action of BFRT at the cellular and morphological levels of the quadriceps.

DESIGN

This will be a randomized, double-blind, placebo-controlled clinical trial.

SETTING

The study will take place at the University of Kentucky and University of Texas Medical Branch.

PARTICIPANTS

Sixty participants between the ages of 15 to 40 years with an ACL tear will be included.

INTERVENTION

Participants will be randomly assigned to (1) physical therapy plus active BFRT (BFRT group) or (2) physical therapy plus placebo BFRT (standard of care group). Presurgical BFRT will involve sessions 3 times per week for 4 weeks, and postsurgical BFRT will involve sessions 3 times per week for 4 to 5 months.

MEASUREMENTS

The primary outcome measure was quadriceps strength (peak quadriceps torque, rate of torque development). Secondary outcome measures included knee biomechanics (knee extensor moment, knee flexion excursion, knee flexion angle), quadriceps muscle morphology (physiological cross-sectional area, fibrosis), and quadriceps muscle physiology (muscle fiber type, muscle fiber size, muscle pennation angle, satellite cell proliferation, fibrogenic/adipogenic progenitor cells, extracellular matrix composition).

LIMITATIONS

Therapists will not be blinded.

CONCLUSIONS

The results of this study may contribute to an improved targeted treatment for the protracted quadriceps strength loss associated with anterior cruciate ligament injury and reconstruction.

Blood Flow Restriction Therapy: From Development to Applications

Blood flow restriction (BFR) has been shown to produce beneficial adaptations to skeletal muscle. These adaptations have been documented in the civilian and military populations. BFR therapy may provide patients a safe method to begin strength training at earlier stages of rehabilitation to allow for earlier and more effective return to activity and improved military readiness. The purpose was to review BFR therapy physiology, complications, side effects, standardized treatment algorithms, and long-term patient outcomes.

Repetitive vascular occlusion stimulus (RVOS) versus standard care to prevent muscle wasting in critically ill patients (ROSProx):a study protocol for a pilot randomised controlled trial

BACKGROUND

Forty per cent of critically ill patients are affected by intensive care unit-acquired weakness (ICU-AW), to which skeletal muscle wasting makes a substantial contribution. This can impair outcomes in hospital, and can cause long-term physical disability after hospital discharge. No effective mitigating strategies have yet been identified. Application of a repetitive vascular occlusion stimulus (RVOS) a limb pressure cuff inducing brief repeated cycles of ischaemia and reperfusion, can limit disuse muscle atrophy in both healthy controls and bed-bound patients recovering from knee surgery. We wish to determine whether RVOS might be effective in mitigating against muscle wasting in the ICU. Given that RVOS can also improve vascular function in healthy controls, we also wish to assess such effects in the critically ill. We here describe a pilot study to assess whether RVOS application is safe, tolerable, feasible and acceptable for ICU patients.

METHODS

This is a randomised interventional feasibility trial. Thirty-two ventilated adult ICU patients with multiorgan failure will be recruited within 48 h of admission and randomised to either the intervention arm or the control arm. Intervention participants will receive RVOS twice daily (except only once on day 1) for up to 10 days or until ICU discharge. Serious adverse events and tolerability (pain score) will be recorded; feasibility of trial procedures will be assessed against pre-specified criteria and acceptability by semi-structured interview. Together with vascular function, muscle mass and quality will be assessed using ultrasound and measures of physical function at baseline, on days 6 and 11 of study enrolment, and at ICU and hospital discharge. Blood and urine biomarkers of muscle metabolism, vascular function, inflammation and DNA damage/repair mechanism will also be analysed. The Health questionnaire will be completed 3 months after hospital discharge.

DISCUSSION

If this study demonstrates feasibility, the derived data will be used to inform the design (and sample size) of an appropriately-powered prospective trial to clarify whether RVOS can help preserve muscle mass/improve vascular function in critically ill patients.

TRIAL REGISTRATION

ISRCTN Registry, ISRCTN44340629. Registered on 26 October 2017.

Progression of Blood Flow Restricted Resistance Training in Older Adults at Risk of Mobility Limitations

Blood flow restriction (BFR) resistance training leads to increased muscle mass and strength but the progression leading to adaptations may be different as strength gains are often to a lesser magnitude than high-load (HL) training. The impact of training loads and repetitions on older adults’ muscle mass and strength following BFR or HL training was evaluated. Twenty-one older adults (67–90 years) classified as being at risk of mobility limitations were randomly assigned to HL (n = 11) or BFR (n = 10) knee extension (KE) and flexion (KF) training twice per week for 12 weeks. Strength was measured with 10-repetition maximum (10-RM) tests and isometric contractions. Cross-sectional area (CSA) of the quadriceps and hamstrings was measured. HL and BFR interventions increased 10-RM KF and isometric strength (P < 0.05) and hamstrings CSA increased an average of 4.8 ± 5.9% after HL and BFR training (time main effect P < 0.01). There were no differences between the training groups (time x group interactions P > 0.05). The rate of progression of KF training load and repetitions was comparable (time × group interactions of each variable P > 0.05). The groups averaged an increase of 0.50 ± 25 kg⋅week^-1 and 1.8 ± 0.1.7 repetitions⋅week^-1 of training (time main effects P < 0.05). The HL training group experienced greater improvements in KE 10-RM strength than the BFR group (60.7 ± 36.0% vs. 35.3 ± 25.5%; P = 0.03). In both groups, isometric KE strength increased 17.3 ± 18.5% (P = 0.001) and there were no differences between groups (P = 0.24). Quadriceps CSA increased (time main effect P < 0.01) and to similar magnitudes (time x group interaction P = 0.62) following HL (6.5 ± 3.1%) and BFR training (7.8 ± 8.2%). The HL group experienced accelerated progression of load when compared to BFR (0.90 ± 0.60 kg⋅week^-1 vs. 30 ± 0.21 kg⋅week^-1; P = 0.006) but was not different when expressed in relative terms. BFR training progressed at a rate of 3.6 ± 1.3 repetitions⋅week^-1 while the HL group progressed at 2.2 ± 0.43 repetitions⋅week^-1 (P = 0.003). HL training led to greater increases in KE 10-RM and it may be attributed to the greater load and/or faster rate of progression of the load throughout the 12-week training period and the specificity of the testing modality. Incorporating systematic load progression throughout BFR training periods should be employed to lead to maximal strength gains.

Blood Flow Restriction Resistance Exercise Improves Muscle Strength and Hemodynamics, but Not Vascular Function in Coronary Artery Disease Patients: A Pilot Randomized Controlled Trial

Resistance training may be associated with unfavorable cardiovascular responses (such as hemodynamic alterations, anginal symptoms or ventricular arrhythmias). In healthy adults, blood flow-restricted (BFR) resistance training improves muscle strength and hypertrophy improvements at lower loads with minimal systemic cardiovascular adverse responses. The aim of this study was to assess the safety and efficacy of BFR resistance training in patients with coronary artery disease (CAD) compared to usual care. Patients with stable CAD were randomized to either 8 weeks of supervised biweekly BFR resistance training (30-40% 1RM unilateral knee extension) or usual exercise routine. At baseline and after 8 weeks, patients underwent 1-RM knee extension tests, ultrasonographic appraisal of vastus lateralis (VL) muscle diameter and of systemic (brachial artery) flow-mediated dilation, and determination of markers of inflammation (CD40 ligand and tumor necrosis factor alfa), and fasting glucose and insulin levels for homeostatic model assessment (HOMA). A total of 24 patients [12 per group, mean age 60 ± 2 years, 6 (25%) women] were included. No training-related adverse events were recorded. At baseline groups significantly differ in age (mean difference: 8.7 years, p < 0.001), systolic blood pressure (mean difference: 12.17 mmHg, p = 0.024) and in metabolic control [insulin (p = 0.014) and HOMA IR (p = 0.014)]. BFR-resistance training significantly increased muscle strength (1-RM, +8.96 kg, p < 0.001), and decreased systolic blood pressure (-6.77 mmHg; p = 0.030), whereas VL diameter (+0.09 cm, p = 0.096), brachial artery flow-mediated vasodilation (+1.55%; p = 0.079) and insulin sensitivity (HOMA IR change of 1.15, p = 0.079) did not improve significantly. Blood flow restricted resistance training is safe and associated with significant improvements in muscle strength, and may be therefore provided as an additional exercise option to aerobic exercise to improve skeletal muscle functioning in patients with CAD. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03087292.

The impact of cuff width and biological sex on cuff preference and the perceived discomfort to blood-flow-restricted arm exercise

OBJECTIVE

To investigate the influence of cuff width, sex, and applied pressure on the perceived discomfort associated with blood flow restriction at rest and following exercise.

APPROACH

Experiment 1 (n  =  96) consisted of four sets of biceps exercise to failure with a narrow and wide cuff inflated to the same relative pressure. Experiment 2 (n  =  87) compared two wide cuffs, one of which was inflated to a relative pressure obtained from a narrow cuff. Experiment 3 (n  =  50) compared the discomfort of wide and narrow cuffs at rest. Effects are presented as median δ (95% credible interval).

MAIN RESULTS

There was no sex effect for any variable of interest. In Experiment 1, the narrow cuff resulted in less discomfort than the wide cuff (39.3 versus 42.5; median δ  -0.388 (-0.670, -0.109)). Participants also rated the narrow cuff as more preferable. Experiment 2 found that a wide cuff inflated to a narrow cuffs pressure resulted in greater discomfort than a wide cuff (44 versus 40.9; median δ: 0.420 (0.118, 0.716)). Experiment 3 found no difference between cuff widths.

SIGNIFICANCE

Blood flow restricted exercise with a narrow cuff results in less discomfort than a wider cuff inflated to the same relative pressure. This effect is not observed at rest and suggests that the wide cuff produces a differential environment compared to a narrow cuff when combined with exercise. Additionally, applying a pressure meant for a narrow cuff to a wide cuff augments the applied pressure and subsequent discomfort to blood flow restricted exercise.

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 Exercise: Considerations of Methodology, Application, and Safety

The current manuscript sets out a position stand for blood flow restriction (BFR) exercise, focusing on the methodology, application and safety of this mode of training. With the emergence of this technique and the wide variety of applications within the literature, the aim of this position stand is to set out a current research informed guide to BFR training to practitioners. This covers the use of BFR to enhance muscular strength and hypertrophy via training with resistance and aerobic exercise and preventing muscle atrophy using the technique passively. The authorship team for this article was selected from the researchers focused in BFR training research with expertise in exercise science, strength and conditioning and sports medicine.

Lactate Stimulates a Potential for Hypertrophy and Regeneration of Mouse Skeletal Muscle

The effects of lactate on muscle mass and regeneration were investigated using mouse skeletal muscle tissue and cultured C2C12 cells. Male C57BL/6J mice were randomly divided into (1) control, (2) lactate (1 mol/L in distilled water, 8.9 mL/g body weight)-administered, (3) cardio toxin (CTX)-injected (CX), and (4) lactate-administered after CTX-injection (LX) groups. CTX was injected into right tibialis anterior (TA) muscle before the oral administration of sodium lactate (five days/week for two weeks) to the mice. Oral lactate administration increased the muscle weight and fiber cross-sectional area, and the population of Pax7-positive nuclei in mouse TA skeletal muscle. Oral administration of lactate also facilitated the recovery process of CTX-associated injured mouse TA muscle mass accompanied with a transient increase in the population of Pax7-positive nuclei. Mouse myoblast-derived C2C12 cells were differentiated for five days to form myotubes with or without lactate administration. C2C12 myotube formation with an increase in protein content, fiber diameter, length, and myo-nuclei was stimulated by lactate. These observations suggest that lactate may be a potential molecule to stimulate muscle hypertrophy and regeneration of mouse skeletal muscle via the activation of muscle satellite cells.

The Association Between Muscle Deoxygenation and Muscle Hypertrophy to Blood Flow Restricted Training Performed at High and Low Loads

The metabolic stress induced by blood flow restriction (BFR) during resistance training (RT) might maximize muscle growth. However, it is currently unknown whether metabolic stress are associated with muscle hypertrophy after RT protocols with high- or low load. Therefore, the aim of the study was to compare the effect of high load RT (HL-RT), high load BFR (HL-BFR), and low load BFR (LL-BFR) on deoxyhemoglobin concentration [HHb] (proxy marker of metabolic stress), muscle cross-sectional area (CSA), activation, strength, architecture and edema before (T1), after 5 (T2), and 10 weeks (T3) of training with these protocols. Additionally, we analyzed the occurrence of association between muscle deoxygenation and muscle hypertrophy. Thirty young men were selected and each of participants’ legs was allocated to one of the three experimental protocols in a randomized and balanced way according to quartiles of the baseline CSA and leg extension 1-RM values of the dominant leg. The dynamic maximum strength was measured by 1-RM test and vastus lateralis (VL) muscle cross-sectional area CSA echo intensity (CSA_echo) and pennation angle (PA) were performed through ultrasound images. The measurement of muscle activation by surface electromyography (EMG) and [HHb] through near-infrared spectroscopy (NIRS) of VL were performed during the training session with relative load obtained after the 1-RM, before (T1), after 5 (T2), and 10 weeks (T3) training. The training total volume (TTV) was greater for HL-RT and HL-BFR compared to LL-BFR. There was no difference in 1-RM, CSA, CSA_echo, CSA_echo/CSA, and PA increases between protocols. Regarding the magnitude of the EMG, the HL-RT and HL-BFR groups showed higher values than and LL-BFR. On the other hand, [HHb] was higher for HL-BFR and LL-BFR. In conclusion, our results suggest that the addition of BFR to exercise contributes to neuromuscular adaptations only when RT is performed with low-load. Furthermore, we found a significant association between the changes in [HHb] (i.e., metabolic stress) and increases in muscle CSA from T2 to T3 only for the LL-BFR, when muscle edema was attenuated.

Blood flow restriction increases myoelectric activity and metabolic accumulation during whole-body vibration

PURPOSE

Whole-body vibration (WBV) training is frequently applied in sports and rehabilitation with the aim of inducing beneficial functional and structural adaptations. In the past decades, blood flow restriction (BFR) training has received increasing attention by enhancing the effectiveness of several low-load exercise regimens. The objective of this study was to evaluate the additional effect of BFR on myoelectric activity and metabolic accumulation during WBV training.

METHODS

Fifteen active men performed three sessions in a counterbalanced order on three different days: whole-body vibration exercise (WBV), whole-body vibration exercise with blood flow restriction (WBV + BFR), and a control session (CON) with neither WBV nor BFR. Electromyographic (EMG) activity was measured in six lower limb muscles throughout each exercise session; lactate and reactive oxygen species (ROS) concentrations were determined prior to, immediately after and 15 min after the exercise sessions.

RESULTS

EMG amplitudes increased from CON (29 ± 13% MVC) to WBV (45 ± 20% MVC) to WBV + BFR (71 ± 37% MVC) conditions (p < 0.05). Likewise, lactate concentrations increased in a similar manner, demonstrating significantly higher increases in the WBV + BFR session compared to WBV and CON. Furthermore, significant correlations between lactate concentration and EMG amplitude were detected. ROS concentration did not change significantly between the conditions.

CONCLUSIONS

The findings of the present study emphasize that the addition of BFR increases the acute effects beyond WBV treatment alone which becomes manifested in both neuromuscular and metabolic adaptations. Further research is needed to identify potential long-term effects of the combination of these two training regimens.

Exercise with blood flow restriction: an effective alternative for the non-pharmaceutical treatment for muscle wasting

Significant muscle wasting is generally experienced by ill and bed rest patients and older people. Muscle wasting leads to significant decrements in muscle strength, cardiorespiratory, and functional capacity, which increase mortality rates. As a consequence, different interventions have been tested to minimize muscle wasting. In this regard, blood flow restriction (BFR) has been used as a novel therapeutic approach to mitigate the burden associated with muscle waste conditions. Evidence has shown that BFR per se can counteract muscle wasting during immobilization or bed rest. Moreover, BFR has also been applied while performing low intensity resistance and endurance exercises and produced increases in muscle strength and mass. Endurance training with BFR has also been proved to increase cardiorespiratory fitness. Thus, frail patients can benefit from exercising with BFR due to the lower cardiovascular and join stress compared with traditional high intensity exercises. Therefore, low intensity resistance and endurance training combined with BFR may be considered as a novel and attractive intervention to counteract muscle wasting and to decrease the burden associated with this condition.

The validity of the EMG and MMG techniques to examine muscle hypertrophy

OBJECTIVE

The purpose of this investigation was to examine the ability of the electromyographic (EMG) and mechanomyographic (MMG) amplitude versus torque relationships to track group and individual changes in muscle hypertrophy as a result of resistance training.

APPROACH

Twelve women performed four weeks of forearm flexion blood flow restriction (BFR) resistance training at a frequency of three times per week. The training was performed at an isokinetic velocity of 120° · s^-1 with a training load that corresponded to 30% of concentric peak torque. Muscle hypertrophy was determined using ultrasound-based assessments of muscle cross-sectional area from the biceps brachii. Training-induced changes in the slope coefficients of the EMG amplitude and MMG amplitude versus torque relationships were determined from the biceps brachii during incremental (10%-100% of maximum) isometric muscle actions.

MAIN RESULTS

There was a significant (p   <  0.001; d  =  2.15) mean training-induced increase in muscle cross-sectional area from 0 week (mean  ±  SD  =  5.86  ±  0.65 cm²) to 4 weeks (7.42  ±  0.80 cm²), a significant (p   =  0.023; d  =  0.36) decrease in the EMG amplitude versus torque relationship (50.70  ±  20.41 to 43.82  ±  17.76 µV · Nm^-1), but no significant (p   =  0.192; d  =  0.17) change in the MMG amplitude versus torque relationship (0.018  ±  0.009 to 0.020  ±  0.009 m · s^-2 · Nm^-1). There was, however, great variability for the individual responses for the EMG and MMG amplitude versus torque relationships.

SIGNIFICANCE

The results of the present study indicated that the EMG amplitude, but not the MMG amplitude versus torque relationship was sensitive to mean changes in muscle cross-sectional area during the early-phase of resistance training. There was, however, great variability for the individual EMG amplitude versus torque relationships that limits its application for identifying individual changes in muscle hypertrophy as a result of BFR.

Jump training with blood flow restriction has no effect on jump performance

This study investigated whether jump training with blood flow restriction (BFR) improves jump performance compared to jump training without BFR under similar exercise intensity in healthy young humans. The participants were twenty healthy males who were assigned to either jump training with BFR (n = 10) or jump training without BFR [control (CON); n = 10] groups. All subjects completed five sets of 10 repetitions with one-minute intervals of half-squat jumps (SJ) at maximal effort, four days a week for four weeks. In the BFR group, circulatory occlusion around both thigh muscles was applied at a pressure of 200 mmHg, and physical characteristics, muscle strength and jump performance were evaluated before and after training. A significant main effect of training period on lean body mass, percentage of body fat and leg circumference in both groups was observed (P < 0.05). For jump training with BFR, only knee flexion strength increased (P < 0.05), while in the CON group, both knee extension and flexion strength increased (P < 0.05). BFR training did not improve SJ or counter-movement jumps (CMJ) (P > 0.05), whereas training without BFR (CON) improved the performance of both jumps (SJ: pre 35.7 ± 5.1 vs. post 38.9 ± 4.1 cm, P = 0.002: CMJ: pre 41.6 ± 3.6 vs. post 44.6 ± 3.8 cm, P < 0.001). These results indicate that jump training with BFR may not be an effective strategy for improving jump performance.

Proximal, Distal, and Contralateral Effects of Blood Flow Restriction Training on the Lower Extremities: A Randomized Controlled Trial

Background:

Blood flow restriction (BFR) training involves low-weight exercises performed under vascular occlusion via an inflatable cuff. For patients who cannot tolerate high-load exercises, BFR training reportedly provides the benefits of high-load regimens, with the advantage of less tissue and joint stress.

Hypothesis:

Low-load BFR training is safe and efficacious for strengthening muscle groups proximal, distal, and contralateral to tourniquet placement in the lower extremities.

Study Design:

Randomized controlled trial.

Level of Evidence:

Level 1.

Methods:

This was a randomized controlled trial of healthy participants completing a standardized 6-week course of BFR training. Patients were randomized to BFR training on 1 extremity or to a control group. Patients were excluded for cardiac, pulmonary, or hematologic disease; pregnancy; or previous surgery in the extremity. Data collected at baseline and completion included limb circumferences and strength testing.

Results:

The protocol was completed by 26 patients, providing 16 BFR and 10 control patients (mean patient age, 27 years; 62% female). A statistically greater increase in strength was seen proximal and distal to the BFR tourniquet when compared with both the nontourniquet extremity and the control group (P < 0.05). Approximately twice the improvement was seen in the BFR group compared with controls. Isokinetic testing showed greater increases in knee extension peak torque (3% vs 11%), total work (6% vs 15%), and average power (4% vs 12%) for the BFR group (P < 0.04). Limb circumference significantly increased in both the thigh (0.8% vs 3.5%) and the leg (0.4% vs 2.8%) compared with the control group (P < 0.01). Additionally, a significant increase occurred in thigh girth (0.8% vs 2.3%) and knee extension strength (3% vs 8%) in the nontourniquet BFR extremity compared with the control group (P < 0.05). There were no reported adverse events.

Conclusion:

Low-load BFR training led to a greater increase in muscle strength and limb circumference. BFR training had similar strengthening effects on both proximal and distal muscle groups. Gains in the contralateral extremity may corroborate a systemic or crossover effect.

Clinical Relevance:

BFR training strengthens muscle groups proximal, distal, and contralateral to cuff placement. Patients undergoing therapy for various orthopaedic conditions may benefit from low-load BFR training with the advantage of less tissue stress.

Improvement of Lower-Body Resistance-Exercise Performance With Blood-Flow Restriction Following Acute Caffeine Intake

PURPOSE

To examine the effects of acute caffeine (CAF) intake on physical performance in 3 sets of unilateral knee extensions with blood-flow restriction.

METHODS

In a double-blind crossover design, 22 trained men ingested 6 mg·kg^-1 of CAF or a placebo (PLA), 1 h prior to performing unilateral knee-extension exercise with blood-flow restriction until exhaustion (30% of 1 maximal repetition).

RESULTS

There was a significant difference in the number of repetitions between the CAF and PLA conditions in the first set (28.3 [5.3] vs 23.7 [3.2]; P = .005), second set (11.6 [3.1] vs 8.9 [2.9]; P = .03), and total repetitions performed across the 3 sets (44.5 [9.4] vs 35.0 [6.6]; P = .001). Blood lactate was also significantly different (P = .03) after exercise between the CAF (7.8 [1.1] mmol·L^-1) and PLA (6.0 [0.9] mmol·L^-1). In regard to pain perception, there was a difference between the CAF and PLA in the second (6.9 [1.5] vs 8.4 [1.4]; P = .04) and third sets (8.7 [0.4] vs 9.5 [0.6]; P = .01). No differences were found for perceived effort.

CONCLUSION

Acute caffeine intake increases performance and blood lactate concentration and reduces perception of pain in unilateral knee-extension exercise with blood-flow restriction.

The combined effect of sprint interval training and postexercise blood flow restriction on critical power, capillary growth, and mitochondrial proteins in trained cyclists

Sprint interval training (SIT) combined with postexercise blood flow restriction (BFR) is a novel method to increase maximal oxygen uptake (V̇o2max) in trained individuals and also provides a potent acute stimulus for angiogenesis and mitochondrial biogenesis. The efficacy to enhance endurance performance, however, has yet to be demonstrated. Trained male cyclists ( n = 21) (V̇o2max: 62.8 ± 3.7 ml·min−1·kg−1) undertook 4 wk of SIT (repeated 30-s maximal sprints) either alone (CON; n = 10) or with postexercise BFR ( n = 11). Before and after training V̇o2max, critical power (CP) and curvature constant ( Wʹ) were determined and muscle biopsies obtained for determination of skeletal muscle capillarity and mitochondrial protein content. CP increased ( P = 0.001) by a similar extent following CON (287 ± 39 W to 297 ± 43 W) and BFR (296 ± 40 W to 306 ± 36 W). V̇o2max increased following BFR by 5.9% ( P = 0.02) but was unchanged after CON ( P = 0.56). All markers of skeletal muscle capillarity and mitochondrial protein content were unchanged following either training intervention. In conclusion, 4 wk of SIT increased CP; however, this was not enhanced further with BFR. SIT was not sufficient to elicit changes in skeletal muscle capillarity and mitochondrial protein content with or without BFR. However, we further demonstrate the potency of combining BFR with SIT to enhance V̇o2max in trained individuals.

NEW & NOTEWORTHY This investigation has demonstrated that 4 wk of sprint interval training (SIT) increased critical power in trained individuals; however, postexercise blood flow restriction (BFR) did not enhance this further. SIT, with or without BFR, did not induce any changes in skeletal muscle capillarity or mitochondrial protein content in our trained population. We do, however, confirm previous findings that SIT combined with BFR is a potent stimulus to enhance maximal oxygen uptake.

Technical and Training Related Aspects of Resistance Training Using Blood Flow Restriction in Competitive Sport - A Review

Blood flow restriction (BFR) combined with resistance training (RT-BFR) shows significant benefits in terms of muscle strength and hypertrophy. Such effects have been observed in clinical populations, in groups of physically active people, and among competitive athletes. These effects are comparable or, in some cases, even more efficient compared to conventional resistance training (CRT). RT-BFR stimulates muscle hypertrophy and improves muscle strength even at low external loads. Since no extensive scientific research has been done in relation to groups of athletes, the aim of the present study was to identify technical, physiological and methodological aspects related to the use of RT-BFR in competitive athletes from various sport disciplines. RT-BFR in groups of athletes has an effect not only on the improvement of muscle strength or muscle hypertrophy, but also on specific motor abilities related to a particular sport discipline. The literature review reveals that most experts do not recommend the use RT-BFR as the only training method, but rather as a complementary method to CRT. It is likely that optimal muscle adaptive changes can be induced by a combination of CRT and RT-BFR. Some research has confirmed benefits of using CRT followed by RT-BFR during a training session. The use of BFR in training also requires adequate progression or modifications in the duration of occlusion in a training session, the ratio of exercises performed with BFR to conventional exercises, the value of pressure or the cuff width.

Resistance training with interval blood flow restriction effectively enhances intramuscular metabolic stress with less ischemic duration and discomfort

Increases in muscle size and strength similar to those obtained with high resistance load can be achieved by combining lower loads with continuous blood flow restriction (BFR). However, high ratings for distress have been reported for continuous BFR. Therefore, we investigated the efficacy (metabolic stress) of BFR applied only during intervals in resistance exercise. Seven healthy men performed three 1-min sets of plantar flexion (30 reps/min) with 1-min rest intervals under 4 conditions: low-load resistance exercise (L, 20% 1-repetition maximum (1RM)) without BFR (L-noBFR), L with BFR during exercise sets (L-exBFR), L with BFR during rest intervals (L-intBFR), and L with continuous BFR during both exercise and rest intervals (L-conBFR). Based on the results of the first experiment, we performed additional protocols using a moderate load (M, 40% 1RM) with intermittent (exercise or rest intervals) BFR (M-exBFR and M-intBFR). Intramuscular metabolic stress, defined as decreases in phosphocreatine and intramuscular pH, was evaluated by ³¹P magnetic resonance spectroscopy. Rated perceived exertion (RPE) was also assessed. At the end of exercise, total decreases in phosphocreatine and intramuscular pH were similar among L-noBFR, L-intBFR, and L-exBFR and significantly less than those in L-conBFR (p < 0.05). In contrast, changes in these variables in M-intBFR but not in M-exBFR were similar to those in L-conBFR. Nevertheless, RPE was lower in M-intBFR than in both M-exBFR and L-conBFR (p < 0.05). The effect of intermittent BFR during exercise might be insufficient to induce metabolic stress when using a low load. However, effective metabolic stress for muscle adaptation could be obtained by moderate-load resistance exercise with BFR during intervals with less ischemic duration and discomfort.

Magnitude of Muscle Strength and Mass Adaptations Between High-Load Resistance Training Versus Low-Load Resistance Training Associated with Blood-Flow Restriction: A Systematic Review and Meta-Analysis

BACKGROUND

Low-load resistance training (< 50% of one-repetition maximum [1RM]) associated with blood-flow restriction (BFR-RT) has been thought to promote increases in muscle strength and mass. However, it remains unclear if the magnitude of these adaptations is similar to conventional high-load resistance training (> 65% 1RM; HL-RT).

OBJECTIVE

To compare the effects of HL- versus BFR-RT on muscle adaptations using a systematic review and meta-analysis procedure.

METHODS

Studies were identified via electronic databases based on the following inclusion criteria: (a) pre- and post-training assessment of muscular strength; (b) pre- and post-training assessment of muscle hypertrophy; (c) comparison of HL-RT vs. BFR-RT; (d) score ≥ 4 on PEDro scale; (e) means and standard deviations (or standard errors) are reported from absolute values or allow estimation from graphs. If this last criterion was not met, data were directly requested from the authors.

RESULTS

The main results showed higher increases in muscle strength for HL- as compared with BFR-RT, even when considering test specificity, absolute occlusion pressure, cuff width, and occlusion pressure prescription. Regarding the hypertrophic response, results revealed similar effects between HL- and BFR-RT, regardless of the absolute occlusion pressure, cuff width, and occlusion pressure prescription.

CONCLUSIONS

Based on the present data, maximum muscle strength may be optimized by specific training methods (i.e., HL-RT) while both HL- and BFR-RT seem equally effective in increasing muscle mass. Importantly, BFR-RT is a valid and effective approach for increasing muscle strength in a wide spectrum of ages and physical capacity, although it may seem particularly of interest for those individuals with physical limitations to engage in HL-RT.

Restrictive Breathing Mask Reduces Repetitions to Failure During a Session of Lower-Body Resistance Exercise

Andre, TL, Gann, JJ, Hwang, PS, Ziperman, E, Magnussen, MJ, and Willoughby, DS. Restrictive breathing mask reduces repetitions to failure during a session of lower-body resistance exercise. J Strength Cond Res 32(8): 2103-2108, 2018-The purpose of this study was to determine the effect of restrictive breathing mask (RBM) on muscle performance, hemodynamic, and perceived stress variables during a session of lower-body resistance exercise. In a crossover design, 10 participants performed 2 separate testing sessions, RBM and no mask, consisting of squat, leg press, and leg extension. The paired-samples t-test was used for session rating of perceived exertion (S-RPE), perceived stress before and after, heart rate (HR), pulse oximetry, and a 2 × 4 (session [mask, no mask] × time [squat exercise, leg press exercise, leg extension exercise, total resistance exercise session]) factorial analysis of variance with repeated measures (p ≤ 0.05). A significant decrease was found in total repetitions during the RBM condition (p < 0.01). A majority of the decrease in repetitions to failure occurred in the squat (p < 0.05) and in the leg press (p < 0.01), whereas no difference was observed in leg extension (p = 0.214). A significant increase was observed in S-RPE during the RBM session (p < 0.01). A significant increase was found in prestress (p < 0.01) and poststress (p = 0.01) in the RBM session. No significant difference existed for HR between exercise sessions (p = 0.08). A significant decrease existed in pulse oximetry during the RBM session (p < 0.01). The use of an RBM had a negative effect on the number of repetitions completed during an acute session of lower-body resistance training.

Sexual Dimorphism in the Estimation of Upper-Limb Blood Flow Restriction in the Seated Position

Borges, A, Teodósio, C, Matos, P, Mil-Homens, P, Pezarat-Correia, P, Fahs, C, and Mendonca, GV. Sexual dimorphism in the estimation of upper-limb blood flow restriction in the seated position. J Strength Cond Res 32(7): 2096-2102, 2018-Arterial occlusion pressure (AOP) is typically used to normalize blood flow restriction (BFR) during low-intensity BFR exercise. Despite strong evidence for sexual dimorphism in muscle blood flow, sex-related differences in AOP estimation remain a controversial topic. We aimed at determining whether the relationship of upper-limb AOP with arm circumference and systolic blood pressure (BP) differs between men and women resting in the seated position. Sixty-two healthy young participants (31 men: 21.7 ± 2.3; 31 women: 22.0 ± 2.0 years) were included in this study. Arm circumference, resting BP, and AOP were taken in the seated position. Multiple linear regression analysis was used to determine whether the relationship of AOP with arm circumference and resting BP differed between sexes. Prediction accuracy was assessed with the mean absolute percent error and Bland-Altman plots. Men had higher systolic BP and larger arm circumference than women (p < 0.05). Nevertheless, AOP was similar between sexes. Arm circumference, systolic BP, and sex were all significant predictors of AOP (p < 0.05), explaining 42% of its variance. The absolute percent error was similar in both sexes (men: -0.55 ± 7.12; women: -0.39 ± 6.31%, p > 0.05). Bland-Altman plots showed that the mean difference between actual and estimated AOP was nearly zero in both groups, with no systematic overestimation or underestimation. In conclusion, arm circumference, systolic BP, and sex are all significant predictors of upper-limb-seated AOP. Their measurement allows for the indirect estimation of BFR pressure within the context of exercise training.

Blood Flow Restriction Training After Achilles Tendon Rupture

Blood flow restriction (BFR) training is a technique shown to be safe and effective at increasing muscular strength and endurance in healthy fitness populations and is under study for its use in postinjury rehabilitation. BFR stimulates muscular strength and hypertrophy gains at much lower loads than traditional methods, allowing patients to begin the rehabilitation process much sooner. We report on 2 patients who incorporated BFR training into their traditional rehabilitation program after Achilles tendon ruptures. Patient 1 was a 29-year-old active duty soldier who sustained a left Achilles tendon rupture while playing competitive football. After operative repair and traditional rehabilitative measures, he was unable to ambulate without assistive devices owing to persistent weakness. The patient subsequently started a 5-week "return to run" program using BFR training. He experienced plantarflexion peak torque improvements of 522% and 108.9% and power gains of 4475% and 211% at 60°/s and 120°/s, respectively. He was able to ambulate without assistive devices at the 5-week follow-up examination. Patient 2 was a 38-year-old male soldier who experienced a complete left Achilles tendon rupture while exercising. After nonoperative treatment with an accelerated rehabilitation program, the patient still experienced significant strength and functional deficits. He was subsequently enrolled in a 6-week course of BFR training. He experienced plantarflexion strength improvements of 55.8% and 47.1% and power gains of 68.8% and 78.7% at 60°/s and 120°/s, respectively. He was able to return to running and sports on completion of 6 weeks of BFR-assisted therapy. Incorporating tourniquet-assisted blood flow restriction with rehabilitation programs can improve strength, endurance, and function after Achilles tendon rupture.

Bench press performance during an intermittent hypoxic resistance training to muscle failure

BACKGROUND

Resistance training performed under hypoxia conditions has been shown to cause major metabolic and hormonal responses. However, the influence of hypoxia on an acute session has been barely studied. The aim of this study was to evaluate the acute effects of an intermittent hypoxic resistance training (IHRT) to muscle failure on bench press performance.

METHODS

A randomized crossover design was performed, and 25 untrained men performed a resistance training under two different conditions: normoxia (FIO2=21%) and high-level hypoxia (FIO2=13%). Resistance training consisted of 3 sets of 75% 1RM to muscle failure, with a 2-minute rest between sets. Physical performance was assessed by quantifying total repetitions, concentric velocity and power variable during all sets. Arterial oxygen saturation, heart rate, rating of perceived exertion (RPE), capillary blood lactate and muscle soreness were also assessed after training.

RESULTS

Physical performance during bench press did not differ under hypoxic conditions (P>0.05). However, there were significant increases (P<0.05) of RPE (from 7.5±0.8 to 7.9±0.8) and blood lactate concentrations (from 5.5±1.2 to 6.2±1.5 mmol/L) in the hypoxia group.

CONCLUSIONS

These findings suggest that hypoxic resistance exercise does not affect exercise performance during bench press exercise. However, influence to perceived exercise intensity and blood lactate concentrations, suggesting that hypoxic resistance training may add substantially to the training dose experienced.

Addition of blood flow restriction to passive mobilization reduces the rate of muscle wasting in elderly patients in the intensive care unit: a within-patient randomized trial

OBJECTIVE:

To evaluate the addition of blood flow restriction to passive mobilization in patients in the intensive care unit.

DESIGN:

The study was a within-patient randomized trial.

SETTING:

Two intensive care units in Belém, from September to October 2017.

SUBJECTS:

In total, 34 coma patients admitted to the intensive care unit sector, and 20 patients fulfilled the study requirements.

INTERVENTIONS:

All participants received the passive mobilization protocol for lower limbs, and blood flow restriction was added only for one side in a concurrent fashion. Intervention lasted the entire patient's hospitalization time.

MAIN OUTCOME MEASUREMENT:

Thigh muscle thickness and circumference.

RESULTS:

In total, 34 subjects were enrolled in the study: 11 were excluded for exclusion criteria, 3 for death, and 20 completed the intervention (17 men and 3 women; mean age: 66 ± 4.3 years). Despite both groups presented atrophy, the atrophy rate was lower in blood flow restriction limb in relation to the control limb (-2.1 vs. -2.8 mm, respectively, in muscle thickness; P = 0.001). In addition, the blood flow restriction limb also had a smaller reduction in the thigh circumference than the control limb (-2.5 vs. -3.6 cm, respectively; P = 0.001).

CONCLUSION:

The use of blood flow restriction did not present adverse effects and seems to be a valid strategy to reduce the magnitude of the rate of muscle wasting that occurs in intensive care unit patients.

Acute effects of whole body vibration combined with blood restriction on electromyography amplitude and hormonal responses

The purpose of this study was to investigate the effects of whole body vibration (WBV) exercise with and without blood flow restriction (BFR) on electromyography (EMG) amplitude and hormonal responses. Eight healthy male adults who lacked physical activity participated in this study and completed 10 sets of WBV and WBV + BFR sessions in a repeated measures crossover design. In the WBV + BFR session, the participants wore a BFR device inflated to 140 mmHg around the proximal region of the thigh muscles. The results indicated that the EMG values from the rectus femoris and vastus lateralis during the WBV + BFR session were significantly higher than those during the WBV session (p < 0.05). Two-way analysis of variance with repeated measures showed that the WBV + BFR and WBV exercise sessions induced a significant (simple main effect for time) increase in lactate (LA) (0.61–4.68 vs. 0.46–3.44 mmol/L) and growth hormone (GH) (0.48–3.85 vs. 0.47–0.82 ng/mL) responses after some of the post-exercise time points (p < 0.05). WBV + BFR elicited significantly higher LA and GH (simple main effect for trial) responses than did WBV after exercise (p < 0.05). Although no significant time × trial interactions were observed for testosterone (T) (604.5–677.75 vs. 545.75–593.88 ng/dL), main effects for trial (p < 0.05) and for time (p < 0.05) were observed. In conclusion, WBV + BFR produced an additive effect of exercise on EMG amplitude and LA and GH responses, but it did not further induce T responses compared to those with WBV alone.

Acute Neuromuscular Adaptations in Response to Low-Intensity Blood-Flow Restricted Exercise and High-Intensity Resistance Exercise: Are There Any Differences?

Fatela, P, Reis, JF, Mendonca, GV, Freitas, T, Valamatos, MJ, Avela, J, and Mil-Homens, P. Acute neuromuscular adaptations in response to low-intensity blood flow restricted exercise and high-intensity resistance exercise: are there any differences? J Strength Cond Res 32(4): 902-910, 2018-Numerous studies have reported similar neuromuscular adaptations between low-intensity (LI) blood-flow restricted exercise (BFRE) and high-intensity (HI) resistance training. Unfortunately, none of these experimental designs individualized blood flow restriction (BFR) levels to each participant. Thus, their findings are difficult to interpret. We aimed at comparing the acute effects of LI BFR (80% of absolute vascular occlusion pressure) with LI non-BFR and HI training on muscle torque, activation, and neuromuscular fatigue. Ten men (23.8 ± 5.4 years) exercised at 20 and 75% of 1 repetition maximum with and without BFR (for LI). Blood flow restriction pressure was determined individually using resting blood-flow measurements. Torque was determined during maximal voluntary contractions (MVCs) at pre-exercise and postexercise time points. Surface electromyographic activity (root mean square [RMS] and median frequency [MF]) was recorded for the rectus femoris (RF) and vastus medialis (VM) muscles, before and after each session of training, during isometric contractions at 20% MVC. Torque decreased post-HI and LI BFR (-9.5 and -7.8%, respectively; p < 0.01), but not after LI non-BFR. The MF was reduced following HI training in the VM and the RF muscles (-5.3 and -12.5%, respectively; p ≤ 0.05). Conversely, the impact of LI BFR on reducing MF was limited to the RF muscle (-10.7%, p ≤ 0.05). Finally, when compared to all other conditions, RMS values were consistently higher during submaximal contractions performed after HI training (p ≤ 0.05). Thus, we conclude that, despite enhancing the acute magnitude of muscular activation and fatigue, LI BFR exercise exerts a less profound impact on neuromuscular function than HI resistance training.

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.

The impact of aerobic exercise training with vascular occlusion in patients with chronic heart failure

AIMS

This study aimed to evaluate the impact of aerobic exercise training with vascular occlusion in patients with chronic heart failure.

METHODS AND RESULTS

Thirty patients with post-infarction heart failure were randomized to an interventional exercise group (IG; n = 15) or a control exercise group (CG; n = 15). Exercise was performed at an intensity of 40-70% of the peak VO2 /W for 6 months. Patients in the IG remained seated on the saddle of the cycle ergometer with their feet on the pedals. Pneumatic tourniquets were applied to the proximal ends of their thighs with appropriate pressure resulting in a 40-80 mmHg increase in the systolic blood pressure that is required for vascular occlusion (208.7 ± 7.4 mmHg). We evaluated the safety and efficacy of the intervention and its effect on exercise capacity and serum BNP levels. There were no significant differences between the IG and CG in patient characteristics at study entry. Peak VO2 /W in the IG significantly increased compared with that in the CG; the change in the serum BNP levels was significantly larger in the IG than in the CG.

CONCLUSIONS

These results suggest that aerobic exercise training with vascular occlusion can improve exercise capacity and serum BNP levels in patients with chronic heart failure.

Muscle fatigue in response to low-load blood flow-restricted elbow-flexion exercise: are there any sex differences?

PURPOSE

This study aimed to determine whether men and women display a different magnitude of muscle fatigue in response to high-load (HL) and low-load blood flow-restricted (LLBFR) elbow-flexion exercise. We also explored to which extent both exercise protocols induce similar levels of muscle fatigue (i.e., torque decrement).

METHODS

Sixty-two young participants (31 men and 31 women) performed dynamic elbow flexions at 20 and 75% of one-repetition maximum for LLBFR and HL exercise, respectively. Maximum voluntary isometric contractions were performed before and after exercise to quantify muscle fatigue.

RESULTS

Men and women exhibited similar magnitude of relative torque decrement after both exercise protocols (p > 0.05). HL was more fatiguing (∆ torque output: 11.9 and 23 N.m in women and men, respectively) than LLBFR resistance exercise (∆ torque output: 8.3 and 15.4 N.m in women and men, respectively) in both sexes, but this was largely attenuated after controlling for the differences in volume load between protocols (p > 0.05).

CONCLUSIONS

These data show that torque decrement in response to LLBFR and HL dynamic elbow-flexion exercise does not follow a sexually dimorphic pattern. Our data also indicate that, if performed in a multiple-set fashion and prescribed for a given volume load, elbow-flexion LLBFR exercise induces similar levels of fatigue as HL acute training. Importantly, this occurs similarly in both sexes.

Low- and high-intensity one-week occlusion training improves muscle oxygen consumption and reduces muscle fatigue

BACKGROUND

Low-intensity resistance exercises with blood flow restriction have been shown is effective to increase muscular strength and hypertrophy. However, the effects of combined training: one-week occlusion training with various exercise intensities by using less occlusion pressure on muscle strength improvement, fatigability and their work capacity are not clear.

METHODS

Participants (N.=24) were middle-distance runners with 4-6 years of training experience. A control group without blood flow restriction (N.=12, age 23±1 years) and an experimental group with blood flow restriction (N.=12, age 22±1 years). In this study, the calf muscles were impacted by the training with occlusion 120 mmHg. We used intensive one-week daily training, whereby exercise intensity was gradually increased daily from 20% to 80% of maximal voluntary contraction (MVC) and then decreased to 60% by the end of the week.

RESULTS

MVC of foot flexion muscles after the one-week occlusion training in the experimental group and control group increased (P<0.05) by 5.6±1.3% and 5.3±1.2%, respectively. Meanwhile in experimental group work capacity improved only 2.4±3.5% (P>0.05) and in control group it significantly decreased 11.8±2.5% (P<0.05). StO2 decreased during exercise test from the baseline 100% to 45.2±4.3% before occlusion training and to 34.6±6.2% after the week of occlusion training (P<0.05).

CONCLUSIONS

Intensive one-week training with occlusion with varying intensity improves resistance to fatigue and recovery after training. This kind of training improves oxygen consumption while exercising.

Spinal and supraspinal control of motor function during maximal eccentric muscle contraction: Effects of resistance training

Neuromuscular activity is suppressed during maximal eccentric (ECC) muscle contraction in untrained subjects owing to attenuated levels of central activation and reduced spinal motor neuron (MN) excitability indicated by reduced electromyography signal amplitude, diminished evoked H-reflex responses, increased autogenic MN inhibition, and decreased excitability in descending corticospinal motor pathways. Maximum ECC muscle force recorded during maximal voluntary contraction can be increased by superimposed electrical muscle stimulation only in untrained individuals and not in trained strength athletes, indicating that the suppression in MN activation is modifiable by resistance training. In support of this notion, maximum ECC muscle strength can be increased by use of heavy-load resistance training owing to a removed or diminished suppression in neuromuscular activity. Prolonged (weeks to months) of heavy-load resistance training results in increased H-reflex and V-wave responses during maximal ECC muscle actions along with marked gains in maximal ECC muscle strength, indicating increased excitability of spinal MNs, decreased presynaptic and/or postsynaptic MN inhibition, and elevated descending motor drive. Notably, the use of supramaximal ECC resistance training can lead to selectively elevated V-wave responses during maximal ECC contraction, demonstrating that adaptive changes in spinal circuitry function and/or gains in descending motor drive can be achieved during maximal ECC contraction in response to heavy-load resistance training.

Muscle hypertrophy following blood flow-restricted, low-force isometric electrical stimulation in rat tibialis anterior: role for muscle hypoxia

Low-force exercise training with blood flow restriction (BFR) elicits muscle hypertrophy as seen typically after higher-force exercise. We investigated the effects of microvascular hypoxia [i.e., low microvascular O2 partial pressures (P mvO2)] during contractions on muscle hypertrophic signaling, growth response, and key muscle adaptations for increasing exercise capacity. Wistar rats were fitted with a cuff placed around the upper thigh and inflated to restrict limb blood flow. Low-force isometric contractions (30 Hz) were evoked via electrical stimulation of the tibialis anterior (TA) muscle. The P mvO2 was determined by phosphorescence quenching. Rats underwent acute and chronic stimulation protocols. Whereas P mvO2 decreased transiently with 30 Hz contractions, simultaneous BFR induced severe hypoxia, reducing P mvO2 lower than present for maximal (100 Hz) contractions. Low-force electrical stimulation (EXER) induced muscle hypertrophy (6.2%, P < 0.01), whereas control group conditions or BFR alone did not. EXER+BFR also induced an increase in muscle mass (11.0%, P < 0.01) and, unique among conditions studied, significantly increased fiber cross-sectional area in the superficial TA ( P < 0.05). Phosphorylation of ribosomal protein S6 was enhanced by EXER+BFR, as were peroxisome proliferator-activated receptor gamma coactivator-1α and glucose transporter 4 protein levels. Fibronectin type III domain-containing protein 5, cytochrome c oxidase subunit 4, monocarboxylate transporter 1 (MCT1), and cluster of differentiation 147 increased with EXER alone. EXER+BFR significantly increased MCT1 expression more than EXER alone. These data demonstrate that microvascular hypoxia during contractions is not essential for hypertrophy. However, hypoxia induced via BFR may potentiate the muscle hypertrophic response (as evidenced by the increased superficial fiber cross-sectional area) with increased glucose transporter and mitochondrial biogenesis, which contributes to the pleiotropic effects of exercise training with BFR that culminate in an improved capacity for sustained exercise.

NEW & NOTEWORTHY We investigated the effects of low microvascular O2 partial pressures (P mvO2) during contractions on muscle hypertrophic signaling and key elements in the muscle adaptation for increasing exercise capacity. Although demonstrating that muscle hypoxia is not obligatory for the hypertrophic response to low-force, electrically induced muscle contractions, the reduced P mvO2 enhanced ribosomal protein S6 phosphorylation and potentiated the hypertrophic response. Furthermore, contractions with blood flow restriction increased oxidative capacity, glucose transporter, and mitochondrial biogenesis, which are key determinants of the pleiotropic effects of exercise training.

Early phase adaptations in muscle strength and hypertrophy as a result of low-intensity blood flow restriction resistance training

PURPOSE

Low-intensity venous blood flow restriction (vBFR) resistance training has been shown to promote increases in muscle strength and size. Eccentric-only muscle actions are typically a more potent stimulus to increase muscle strength and size than concentric-only muscle actions performed at the same relative intensities. Therefore, the purpose of this investigation was to examine the time-course of changes in muscle strength, hypertrophy, and neuromuscular adaptations following 4 weeks of unilateral forearm flexion low-intensity eccentric vBFR (Ecc-vBFR) vs. low-intensity concentric vBFR (Con-vBFR) resistance training performed at the same relative intensity.

METHODS

Thirty-six women were randomly assigned to either Ecc-vBFR (n = 12), Con-vBFR (n = 12) or control (no intervention, n = 12) group. Ecc-vBFR trained at 30% of eccentric peak torque and Con-vBFR trained at 30% of concentric peak torque. All training and testing procedures were performed at an isokinetic velocity of 120° s^-¹.

RESULTS

Muscle strength increased similarly from 0 to 2 and 4 weeks of training as a result of Ecc-vBFR (13.9 and 35.0%) and Con-vBFR (13.4 and 31.2%), but there were no changes in muscle strength for the control group. Muscle thickness increased similarly from 0 to 2 and 4 weeks of training as a result of Ecc-vBFR (11.4 and 12.8%) and Con-vBFR (9.1 and 9.9%), but there were no changes for the control group. In addition, there were no changes in any of the neuromuscular responses.

CONCLUSIONS

The Ecc-vBFR and Con-vBFR low-intensity training induced comparable increases in muscle strength and size. The increases in muscle strength, however, were not associated with neuromuscular adaptations.

Hemodynamic responses are reduced with aerobic compared with resistance blood flow restriction exercise

The hemodynamics of light‐load exercise with an applied blood‐flow restriction (BFR) have not been extensively compared between light‐intensity, BFR, and high‐intensity forms of both resistance and aerobic exercise in the same participant population. Therefore, the purpose of this study was to use a randomized crossover design to examine the hemodynamic responses to resistance and aerobic BFR exercise in comparison with a common high‐intensity and light‐intensity non‐BFR exercise. On separate occasions participants completed a leg‐press (resistance) or treadmill (aerobic) trial. Each trial comprised a light‐intensity bout (LI) followed by a light‐intensity bout with BFR (80% resting systolic blood pressure (LI+BFR)), then a high‐intensity bout (HI). To characterize the hemodynamic response, measures of cardiac output, stroke volume, heart rate and blood pressure were taken at baseline and exercise for each bout. Exercising hemodynamics for leg‐press LI+BFR most often resembled those for HI and were greater than LI (e.g. for systolic blood pressure LI+BFR = 152 ± 3 mmHg; HI = 153 ± 3; LI = 143 ± 3 P < 0.05). However, exercising hemodynamics for treadmill LI+BFR most often resembled those for LI and were lower than HI (e.g. for systolic pressure LI+BFR = 124 ± 2 mmHg; LI = 123 ± 2; HI = 140 ± 3 P < 0.05). In conclusion, the hemodynamic response for light aerobic (walking) BFR exercise suggests this mode of BFR exercise may be preferential for chronic use to develop muscle size and strength, and other health benefits in certain clinical populations that are contraindicated to heavy‐load resistance exercise.

Lactate increases myotube diameter via activation of MEK/ERK pathway in C2C12 cells

AIM

Lactate is produced in and released from skeletal muscle cells. Lactate receptor, G-protein-coupled receptor 81 (GPR81), is expressed in skeletal muscle cells. However, a physiological role of extracellular lactate on skeletal muscle is not fully clarified. The purpose of this study was to investigate extracellular lactate-associated morphological changes and intracellular signals in C2C12 skeletal muscle cells.

METHODS

Mouse myoblast C2C12 cells were differentiated for 5 days to form myotubes. Sodium lactate (lactate) or GPR81 agonist, 3,5-dihydroxybenzoic acid (3,5-DHBA), was administered to the differentiation medium.

RESULTS

Lactate administration increased the diameter of C2C12 myotubes in a dose-dependent manner. Administration of 3,5-DHBA also increased myotube diameter. Not only lactate but also 3,5-DHBA upregulated the phosphorylation level of mitogen-activated protein kinase kinase 1/2 (MEK1/2), p42/44 extracellular signal-regulated kinase-1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK). MEK inhibitor U0126 depressed the phosphorylation of ERK-p90RSK and increase in myotube diameter induced by lactate. On the other hand, both lactate and 3,5-DHBA failed to induce significant responses in the phosphorylation level of Akt, mammalian target of rapamycin, p70 S6 kinase and protein degradation-related signals.

CONCLUSION

These observations suggest that lactate-associated increase in the diameter of C2C12 myotubes is induced via activation of GRP81-mediated MEK/ERK pathway. Extracellular lactate might have a positive effect on skeletal muscle size.

Mild exercise along with limb blood-flow restriction modulates the electrocardiogram, angiotensin, and apelin receptors of the heart in aging rats

OBJECTIVES

Considering the lack of information, the effects of mild endurance exercise plus blood flow restriction (BFR) on electrocardiographic parameters, hypertrophy index, and expression of angiotensin II receptors type 1 (AT1R) and type 2 (AT2R) and apelin receptor (APJ) were assessed in hearts of old male rats.

MATERIALS AND METHODS

Animal were grouped as control (CTL), Sham (Sh), lower extremities blood flow restriction (BFR), exercise (Ex), Sham + exercise (Sh + Ex), and blood flow restriction + exercise (BFR + Ex).

RESULTS

Exercise plus BFR significantly decreased the corrected QT (QTc) interval (P<0.01 vs CTL and Sh groups) and increased the heart hypertrophy index (P<0.05 vs CTL and BFR groups). Exercise alone increased expression of the APJ (P<0.01, vs CTL, Sh, and BFR groups) and AT2 receptors (P<0.001, vs Sh, CTL, BFR, and BFR + exercise groups), whereas it reduced expression of AT1R (P<0.01 in comparison with CTL, Sh, and BFR groups). Exercise plus BFR caused a significant increase in APJ (P<0.05 vs Ex, Sh+Ex and P<0.001 vs CTL, Sh, and BFR groups) and also expression of AT1R (P<0.001 vs Ex, Sh + Ex, CTL, Sh, and P<0.01 vs BFR groups). Accompaniment of exercise with BFR destroyed the effect of exercise on the expression of AT2R.

CONCLUSION

Mild endurance exercise plus BFR can alter the expression of angiotensin II and apelin receptors that leads to cardiac hypertrophy and improves the ventricular conductivity of aging rats.