Venous blood gas and metabolite response to low-intensity muscle contractions with external limb compression

Minimum velocity threshold in response to the free-weight back squat: reliability and validity of different submaximal loading schemes

PURPOSE

To explore if mean concentric velocity (MCV) of the last repetition before set failure differs between free-weight back squat protocols with greater emphasis on metabolic accumulation vs. mechanical loading. The between-set and between-day reliability of terminal MCV obtained with these different loading schemes was also determined.

METHODS

Fifteen healthy male participants (18-30 years) were included. They all were required to exhibit a relative strength ≥ 1.5 times their body mass. MCVs were obtained at one-repetition maximum (1RM) and with two submaximal protocols (metabolic emphasis: three sets of 40%1RM with blood-flow restriction vs. mechanical emphasis: three sets 80%1RM without blood-flow restriction). Participants were instructed to reach maximal intended concentric velocity in each repetition up to failure.

RESULTS

Set failure was achieved at a faster MCV with the metabolic protocol (p < 0.05). The reliability of MCV at failure reached higher values for the metabolic loading scheme. However, while the MCV achieved at failure during the metabolic protocol was systematically higher than the MCV at 1RM (p < 0.05), this was not entirely the case for the mechanical protocol (similar to 1RM MCV during the last sets in both testing days). Finally, the absolute error derived from estimating the MCV at 1RM based on the MCV obtained at set failure with the mechanical protocol was considerably high (≥ 0.05 m/s).

CONCLUSION

This study indicates that MCV obtained at set failure is dependent on the specificity of the physiological demands of exercise. Thus, MCVs obtained at failure with submaximal loads should not be used to estimate 1RM MCV.

The Discrepancy Between External and Internal Load/Intensity during Blood Flow Restriction Exercise: Understanding Blood Flow Restriction Pressure as Modulating Factor

Physical exercise induces acute psychophysiological responses leading to chronic adaptations when the exercise stimulus is applied repeatedly, at sufficient time periods, and with appropriate magnitude. To maximize long-term training adaptations, it is crucial to control and manipulate the external load and the resulting psychophysiological strain. Therefore, scientists have developed a theoretical framework that distinguishes between the physical work performed during exercise (i.e., external load/intensity) and indicators of the body's psychophysiological response (i.e., internal load/intensity). However, the application of blood flow restriction (BFR) during exercise with low external loads/intensities (e.g., ≤ 30% of the one-repetition-maximum, ≤ 50% of maximum oxygen uptake) can induce physiological and perceptual responses, which are commonly associated with high external loads/intensities. This current opinion aimed to emphasize the mismatch between external and internal load/intensity when BFR is applied during exercise. In this regard, there is evidence that BFR can be used to manipulate both external load/intensity (by reducing total work when exercise is performed to exhaustion) and internal load/intensity (by leading to higher physiological and perceptual responses compared to exercise performed with the same external load/intensity without BFR). Furthermore, it is proposed to consider BFR as an additional exercise determinant, given that the amount of BFR pressure can determine not only the internal but also external load/intensity. Finally, terminological recommendations for the use of the proposed terms in the scientific context and for practitioners are given, which should be considered when designing, reporting, discussing, and presenting BFR studies, exercise, and/or training programs.

Impact of Complete Intermittent Blood Flow Restriction in Upper Limbs Strength and Neural Function

Purpose: We aimed to investigate the chronic effects of low-load strength training (LT) with complete intermittent blood flow restriction (IBFR) on neural adaptations and strength in biceps brachii. Methods: Nineteen volunteers were randomly assigned into two different 9-week training protocols consisting of three assessment weeks and six training weeks: (a) LT with complete IBFR (LT-IBFR; n = 10) and (b) LT without complete IBFR (LT; n = 9). Strength was evaluated by predicted 1 repetition maximum (1RM) at weeks 1, 5, and 9 and neural function by root mean square (RMS) and median frequency (MDF) at sessions 1, 7, and 12 during the first three and last three repetitions. Both groups performed three sets of Scott curl with 20% of predicted 1RM interspersed with 90s rest twice a week. Results: No changes were found in predicted 1RM throughout the training protocols nor between groups. LT-IBFR group showed lower RMS in the first set than LT for the first three repetitions and higher RMS in all sets for the last three repetitions with decreases in this value across the sets with no longitudinal changes for both groups. MDF in the first three repetitions did not differentiate between groups, however, in the last three repetitions, MDF were lower for LTIBFR group in all sets and it increased across the sets for this condition with no chronical changes for both groups in both repetitions zones. These results suggest that LT-IBFR may be ineffective for increasing Q5 strength and it did not promote chronic neural adaptations.

The Effects of Blood Flow Restriction Aerobic Exercise on Body Composition, Muscle Strength, Blood Biomarkers, and Cardiovascular Function: A Narrative Review

Blood flow restriction exercise has emerged as a promising alternative, particularly for elderly individuals and those unable to participate in high-intensity exercise. However, existing research has predominantly focused on blood flow restriction resistance exercise. There remains a notable gap in understanding the comprehensive effects of blood flow restriction aerobic exercise (BFRAE) on body composition, lipid profiles, glycemic metabolism, and cardiovascular function. This review aims to explore the physiological effects induced by chronic BFRAE. Chronic BFRAE has been shown to decrease fat mass, increase muscle mass, and enhance muscular strength, potentially benefiting lipid profiles, glycemic metabolism, and overall function. Thus, the BFRAE offers additional benefits beyond traditional aerobic exercise effects. Notably, the BFRAE approach may be particularly suitable for individuals with low fitness levels, those prone to injury, the elderly, obese individuals, and those with metabolic disorders.

Effect of blood flow restriction training on health promotion in middle-aged and elderly women: a systematic review and meta-analysis

Background: Physical activities play an important role in alleviating the aging problem and improving the physical fitness of middle-aged and elderly people. Blood flow restriction (BFR) training, also known as pressure training, has been widely used to improve athletes' performance and rehabilitation, which is a relatively novel exercise method for improving the physical fitness of middle-aged and elderly people. The purpose of this study is to conduct a systematic review and meta-analysis of domestic and foreign randomized controlled trial studies on BFR training for middle-aged and elderly women, further explore the impact of BFR training on health status. Methods: Meta-analysis was performed according to PRISMA standards, and charts were drawn using Review Manager 5.4 and Stata 17 software. In this study, the keywords such as "pressure training", "blood restriction training", "elderly women", "KAATSU", "blood flow restriction training" were used on CNKI, China Science and Technology Journal Database, PubMed, Embase, Web of Science, Cochrane Library, EBSCO, Scopus, and randomized controlled trials were searched in all languages. The search was performed from the establishment of database to 2 January 2024. The results of the combined effect were represented by standard mean differences. Results: Among the 681 literature retrieved, six eligible English articles were included in this meta-analysis. The overall effect test of the combined effect was performed on 10 groups of data, and the results were SMD = -0.18 (95%CI: -0.91 to 0.56; p > 0.05), the maximum dynamic force of 1RM SMD = 0.97 (95%CI: 0.35 to 1.58; p < 0.05), leg compression force SMD = -0.10 (95%CI: -0.78 to 0.57; p > 0.05), heart rate SMD = 0.33 (95%CI: -2.50 to 3.17; p > 0.05), systolic blood pressure (SBP) SMD = -1.44 (95%CI: -2.17 to -0.70; p < 0.05), diastolic blood pressure (DBP) SMD = -0.69 (95%CI: 2.54 to 1.15; p > 0.05). Conclusion: BFR training had a significant effect on the increase of the maximum dynamic force of 1RM and decrease of blood pressure in middle-aged and elderly women, but there was no significant difference found in heart rate and leg compression force. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42024491642.

Muscle activity and hypoalgesia in blood flow restricted versus unrestricted effort-matched resistance exercise in healthy adults

This study assessed muscle activity (root mean square, RMS, and median frequency, MDF) to evaluate the acute response to blood flow restriction (BFR) resistance exercise (RE) and conventional moderate intensity (MI) RE. We also performed exploratory analyses of differences based on sex and exercise-induced hypoalgesia (EIH). Fourteen asymptomatic individuals performed four sets of unilateral leg press with their dominant leg to volitional fatigue under two exercise conditions: BFR RE and MI RE. Dominant side rectus femoris (RF) and vastus lateralis (VL) muscle activity were measured using surface electromyography (sEMG) through exercise. RMS and MDF were calculated and compared between conditions and timepoints using a linear mixed model. Pressure pain thresholds (PPT) were tested before and immediately after exercise and used to quantify EIH. Participants were then divided into EIH responders and nonresponders, and the differences on RMS and MDF were compared between the two groups using Hedges' g. RMS significantly increased over time (RF: p = 0.0039; VL: p = 0.001) but not between conditions (RF: p = 0.4; VL: p = 0.67). MDF decreased over time (RF: p = 0.042; VL: p < 0.001) but not between conditions (RF: p = 0.74; VL: p = 0.77). Consistently lower muscle activation was found in females compared with males (BRF, RF: g = 0.63; VL, g = 0.5. MI, RF: g = 0.72; VL: g = 1.56), with more heterogeneous findings in MDF changes. For BFR, EIH responders showed greater RMS changes (Δ RMS) (RF: g = 0.90; VL: g = 1.21) but similar MDF changes (Δ MDF) (RF: g = 0.45; VL: g = 0.28) compared to nonresponders. For MI, EIH responders demonstrated greater increase on Δ RMS (g = 0.61) and decrease on Δ MDF (g = 0.68) in RF but similar changes in VL (Δ RMS: g = 0.40; Δ MDF: g = 0.39). These results indicate that when exercising to fatigue, no statistically significant difference was observed between BFR RE and conventional MI RE in Δ RMS and Δ MDF. Lower muscle activity was noticed in females. While exercising to volitional fatigue, muscle activity may contribute to EIH.

Influence of Blood Flow Restriction on Neuromuscular Function and Fatigue During Forearm Flexion in Men

ABSTRACT

Montgomery, TR Jr, Olmos, A, Sears, KN, Succi, PJ, Hammer, SM, Bergstrom, HC, Hill, EC, Trevino, MA, and Dinyer-McNeely, TK. Influence of blood flow restriction on neuromuscular function and fatigue during forearm flexion in men. J Strength Cond Res 38(7): e349-e358, 2024-To determine the effects of blood flow restriction (BFR) on the mean firing rate (MFR) and motor unit action potential amplitude (MUAPAMP) vs. recruitment threshold (RT) relationships during fatiguing isometric elbow flexions. Ten men (24.5 ± 4.0 years) performed isometric trapezoidal contractions at 50% maximum voluntary contraction to task failure with or without BFR, on 2 separate days. For BFR, a cuff was inflated to 60% of the pressure required for full brachial artery occlusion at rest. During both visits, surface electromyography was recorded from the biceps brachii of the dominant limb and the signal was decomposed. A paired-samples t test was used to determine the number of repetitions completed between BFR and CON. ANOVAs (repetition [first, last] × condition [BFR, CON]) were used to determine differences in MFR vs. RT and MUAPAMP vs. RT relationships. Subjects completed more repetitions during CON (12 ± 4) than BFR (9 ± 2; p = 0.012). There was no significant interaction (p > 0.05) between the slopes and y-intercepts during the repetition × condition interaction for MUAPAMP vs. MFR. However, there was a main effect of repetition for the slopes of the MUAPAMP vs. RT (p = 0.041) but not the y-intercept (p = 0.964). Post hoc analysis (collapsed across condition) indicated that the slopes of the MUAPAMP vs. RT during the first repetition was less than the last repetition (first: 0.022 ± 0.003 mv/%MVC; last: 0.028 ± 0.004 mv/%MVC; p = 0.041). Blood flow restriction resulted in the same amount of higher threshold MU recruitment in approximately 75% of the repetitions. Furthermore, there was no change in MFR for either condition, even when taken to task failure. Thus, BFR training may create similar MU responses with less total work completed than training without BFR.

Blood flow restriction increases necessary muscle excitation of the elbow flexors during a single high-load contraction

PURPOSE

To investigate the effects of blood flow restriction (BFR) on electromyographic amplitude (EMGRMS)-force relationships of the biceps brachii (BB) during a single high-load muscle action.

METHODS

Twelve recreationally active males and eleven recreationally active females performed maximal voluntary contractions (MVCs), followed by an isometric trapezoidal muscle action of the elbow flexors at 70% MVC. Surface EMG was recorded from the BB during BFR and control (CON) visits. For BFR, cuff pressure was 60% of the pressure required to completely occlude blood at rest. Individual b (slope) and a terms (gain) were calculated from the log-transformed EMGRMS-force relationships during the linearly increasing and decreasing segments of the trapezoid. EMGRMS during the steady force segment was normalized to MVC EMGRMS.

RESULTS

For BFR, the b terms were greater during the linearly increasing segment than the linearly decreasing segment (p < 0.001), and compared to the linearly increasing segment for CON (p < 0.001). The a terms for BFR were greater during the linearly decreasing than linearly increasing segment (p = 0.028). Steady force N-EMGRMS was greater for BFR than CON collapsed across sex (p = 0.041).

CONCLUSION

BFR likely elicited additional recruitment of higher threshold motor units during the linearly increasing- and steady force-segment. The differences between activation and deactivation strategies were only observed with BFR, such as the b terms decreased and the a terms increased for the linearly decreasing segment in comparison to the increasing segment. However, EMGRMS-force relationships during the linearly increasing- and decreasing-segments were not different between sexes during BFR and CON.

Intermittent blood flow restriction with low-load resistance training for older adults with knee osteoarthritis: a randomized, controlled, non-inferiority trial protocol

BACKGROUND

Knee osteoarthritis (KOA) is a chronic musculoskeletal disorder characterized by pain and functional impairment. Blood flow restriction (BFR) with low-load resistance training (LLRT) demonstrates a similar improvement in clinical outcomes to high-load resistance training (HLRT) in treating KOA. It has not been established whether intermittent blood flow restriction (iBFR) with LLRT can lead to clinical outcomes that are comparable to those produced by continuous blood flow restriction (cBFR) with LLRT and HLRT. The aim of the proposed study is to evaluate the efficacy of iBFR with LLRT on pain, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), muscle strength, muscle mass, physical function, perceptions of discomfort and effort, and adherence in KOA patients.

METHODS

This is a three-arm, non-inferiority, randomized controlled trial utilizing blinded assessors. Two hundred thirteen participants will be randomly allocated to one of the following three groups: iBFR group-receiving 4 months of LLRT with iBFR, twice weekly (n = 71); cBFR group-receiving 4 months of LLRT with cBFR, twice weekly (n = 71); or HLRT group-receiving 4 months of HLRT without BFR, twice weekly (n = 71). The primary outcome is pain. The secondary outcomes include the WOMAC, muscle strength, muscle mass, physical function, perceptions of discomfort and effort, and adherence. Pain and WOMAC will be measured at the baseline and 4 and 12 months after randomizations. Muscle strength, muscle mass, and physical function will be measured at the baseline and 4 months after randomizations. The perceptions of discomfort and effort will be measured during the first and final sessions.

DISCUSSION

BFR with LLRT has a similar improvement in clinical outcomes as HLRT. However, cBFR may cause elevated ratings of perceived exertion and local discomfort, compromising patient tolerability and treatment adherence. If iBFR with LLRT could produce improvement in clinical outcomes analogous to those of HLRT and iBFR with LLRT, it could be considered an alternative approach for treating patients with KOA.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300072820. Registered on June 26, 2023.

Dose-dependent nonthermal modulation of whole body heat exchange during dynamic exercise in humans

To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate whole body dry and evaporative heat exchange. These responses are modulated by the rise in body temperature (thermal factors), as well as several nonthermal factors implicated in the cardiovascular response to exercise (i.e., central command, mechanoreceptors, and metaboreceptors). However, the way these nonthermal factors interact with thermal factors to maintain heat balance remains poorly understood. We therefore used direct calorimetry to quantify the effects of dose-dependent increases in the activation of these nonthermal stimuli on whole body dry and evaporative heat exchange during dynamic exercise. In a randomized crossover design, eight participants performed 45-min cycling at a fixed metabolic heat production (200 W/m2) in warm, dry conditions (30°C, 20% relative humidity) on four separate occasions, differing only in the level of lower-limb compression applied via bilateral thigh cuffs pressurized to 0, 30, 60, or 90 mmHg. This model provoked increments in nonthermal activation while ensuring the heat loss required to balance heat production was matched across trials. At end-exercise, dry heat loss was 2 W/m2 [1, 3] lower per 30-mmHg pressure increment (P = 0.006), whereas evaporative heat loss was elevated 5 W/m2 [3, 7] with each pressure increment (P < 0.001). Body heat storage and esophageal temperature did not differ across conditions (both P ≥ 0.600). Our findings indicate that the nonthermal factors engaged during exercise exert dose-dependent, opposing effects on whole body dry and evaporative heat exchange, which do not significantly alter heat balance.NEW & NOTEWORTHY To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate dry and evaporative heat exchange. These responses are modulated by body temperatures (thermal factors) and several nonthermal factors (e.g., central command, metaboreceptors), although the way thermal and nonthermal factors interact to regulate body temperature is poorly understood. We demonstrate that nonthermal factors exert dose-dependent, opposing effects on dry and evaporative heat loss, without altering heat storage during dynamic exercise.

Effects of blood flow restriction training on sports performance in athletes: a systematic review with meta-analysis

INTRODUCTION

Blood flow restriction training (BFRT) is an effective training method to improve sports performance in healthy athletes. Nevertheless, a systematic review with meta-analysis regarding how BFRT affects sports performance in athletes is still lacking. Consequently, the study attempted to expand and consolidate the prior studies regarding the effect of BFRT on technical and physical performance in athletes.

EVIDENCE ACQUISITION

This study was based on PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyzes) statement guidelines for a systematic review of the academic databases Scopus, Web of Science, PubMed, EBSCOhost (SportDiscus), and Google Scholar. The PEDro scale was used to assess the methodological quality of the included publications, which ranged from moderate to high quality. The systematic review protocol was registered on inplasy.com (INPLASY202380049).

EVIDENCE SYNTHESIS

Out of 249 studies identified, 93 articles were evaluated as eligible, and after the screening, 18 studies were finally included in this systematic review. Meta-analysis results showed a significant enhancement on vertical jump height in the BFRT group compared to the control group (SMD=1.39, 95% CI=0.30-2.49, P=0.01). BFRT was able to significantly increase maximal oxygen uptake (SMD=1.65, 95% CI=0.56-2.74, P<0.01). While no significant improvement in sprint time was observed (SMD= -0.18, 95% CI=-1.18-0.82, P=0.115).

CONCLUSIONS

The finding suggests that BFRT is beneficial to athletes as this training method can be effective in enhancing physical and technical performance in athletes. Nevertheless, further analysis needs to be conducted to fully determine the effectiveness of the moderators of the intervention on sports performance.

Muscle strength adaptation between high-load resistance training versus low-load blood flow restriction training with different cuff pressure characteristics: a systematic review and meta-analysis

Purpose: In this systematic review and meta-analysis, blood flow restriction (BFR) with low-load resistance training (BFR-RT) was compared with high-load resistance training (HL-RT) on muscle strength in healthy adults. The characteristics of cuff pressure suitable for muscle strength gain were also investigated by analyzing the effects of applying different occlusion pressure prescriptions and cuff inflation patterns on muscle strength gain. Methods: Literature search was conducted using PubMed, Ovid Medline, ProQuest, Cochrane Library, Embase, and Scopus databases to identify literature published until May 2023. Studies reporting the effects of BFR-RT interventions on muscle strength gain were compared with those of HL-RT. The risk of bias in the included trials was assessed using the Cochrane tool, followed by a meta-analysis to calculate the combined effect. Subgroup analysis was performed to explore the beneficial variables. Results: Nineteen articles (42 outcomes), with a total of 458 healthy adults, were included in the meta-analysis. The combined effect showed higher muscle strength gain with HL-RT than with BFR-RT (p = 0.03, SMD = -0.16, 95% CI: -0.30 to -0.01). The results of the subgroup analysis showed that the BFR-RT applied with incremental and individualized pressure achieved muscle strength gain similar to the HL-RT (p = 0.8, SMD = -0.05, 95% CI: -0.44 to 0.34; p = 0.68, SMD = -0.04, 95% CI: -0.23 to 0.15), but muscle strength gain obtained via BFR-RT applied with absolute pressure was lower than that of HL-RT (p < 0.05, SMD = -0.45, 95% CI: -0.71 to -0.19). Furthermore, muscle strength gain obtained by BFR-RT applied with intermittent pressure was similar to that obtained by HL-RT (p = 0.88, SMD = -0.02, 95% CI: -0.27 to 0.23), but muscle strength gain for BFR-RT applied with continuous pressure showed a less prominent increase than that for HL-RT (p < 0.05, SMD = -0.3, 95% CI: -0.48 to -0.11). Conclusion: In general, HL-RT produces superior muscle strength gains than BFR-RT. However, the application of individualized, incremental, and intermittent pressure exercise protocols in BFR-RT elicits comparable muscle strength gains to HL-RT. Our findings indicate that cuff pressure characteristics play a significant role in establishing a BFR-RT intervention program for enhancing muscle strength in healthy adults. Clinical Trial Registration: https://www.crd.york.ac.uk/PROSPERO/#recordDetails; Identifier: PROSPERO (CRD42022364934).

The Effect of Skeletal Muscle Oxygenation on Hemodynamics, Cerebral Oxygenation and Activation, and Exercise Performance during Incremental Exercise to Exhaustion in Male Cyclists

This study aimed to elucidate whether muscle blood flow restriction during maximal exercise is associated with alterations in hemodynamics, cerebral oxygenation, cerebral activation, and deterioration of exercise performance in male participants. Thirteen healthy males, cyclists (age 33 ± 2 yrs., body mass: 78.6 ± 2.5 kg, and body mass index: 25.57 ± 0.91 kg·m^-1), performed a maximal incremental exercise test on a bicycle ergometer in two experimental conditions: (a) with muscle blood flow restriction through the application of thigh cuffs inflated at 120 mmHg (with cuffs, WC) and (b) without restriction (no cuffs, NC). Exercise performance significantly deteriorated with muscle blood flow restriction, as evidenced by the reductions in V˙O_2max (-17 ± 2%, p < 0.001), peak power output (-28 ± 2%, p < 0.001), and time to exhaustion (-28 ± 2%, p < 0.001). Muscle oxygenated hemoglobin (Δ[O₂Hb]) during exercise declined more in the NC condition (p < 0.01); however, at exhaustion, the magnitude of muscle oxygenation and muscle deoxygenation were similar between conditions (p > 0.05). At maximal effort, lower cerebral deoxygenated hemoglobin (Δ[HHb]) and cerebral total hemoglobin (Δ[THb]) were observed in WC (p < 0.001), accompanied by a lower cardiac output, heart rate, and stroke volume vs. the NC condition (p < 0.01), whereas systolic blood pressure, rating of perceived exertion, and cerebral activation (as assessed by electroencephalography (EEG) activity) were similar (p > 0.05) between conditions at task failure, despite marked differences in exercise duration, maximal aerobic power output, and V˙O_2max. In conclusion, in trained cyclists, muscle blood flow restriction during an incremental cycling exercise test significantly limited exercise performance. Exercise intolerance with muscle blood flow restriction was mainly associated with attenuated cardiac responses, despite cerebral activation reaching similar maximal levels as without muscle blood flow restriction.

Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults

PURPOSE

The purpose of this study was to examine the physiological responses resulting from an acute blood flow restriction resistance exercise bout with two different cuff pressures in young, healthy men and women.

METHODS

Thirty adults (18-30 yr) completed a bilateral leg extension blood flow restriction bout consisting of four sets (30-15-15-15 repetitions), with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and EMG amplitude (EMG AMP) were collected from the dominant or nondominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVA models were used to examine mean differences in the change in EMG AMP and NIRS parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A P value ≤0.05 was considered statistically significant.

RESULTS

Regardless of sex or cuff pressure, the change in EMG AMP was lower in set 1 (14.8%) compared with the remaining sets (22.6%-27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP, there was an effect for time such that MAP increased from preexercise (87.5 ± 4.3 mm Hg) to postexercise (104.5 ± 4.1 mm Hg).

CONCLUSIONS

The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the interset rest. In addition, there did not seem to be any meaningful sex-related difference in this sample of young healthy adults.

Acute effects of blood flow restriction with whole-body vibration on sprint, muscle activation and metabolic accumulation in male sprinters

Purpose: The aim of this study was to explore the acute effects of Blood Flow Restriction Training (BFRT), Whole-Body Vibration (WBV), and BFRT + WBV on the 20 m sprint, muscle activation, and metabolic accumulation in male sprinters.

Method: Sixteen male sprinters randomly performed BFRT, WBV, or BFRT + WBV interventions with 72 h intervals. Electromyography (EMG) signals were collected before and during interventions. Fingertip blood was taken before, immediately after, and 15 min after the intervention. 20 m sprint was performed before and 3 min after the intervention.

Results: 1) 0–10m and 0–20 m sprint performance were significantly improved after WBV and BFRT + WBV interventions (p &lt; 0.05), 0–20 m sprint performance was significantly improved after all three interventions (p &lt; 0.05), 2) After BFRT + WBV intervention, the EMG amplitude of the vastus lateralis and soleus were significantly improved. Greater increases in EMG activity of the tibialis anterior muscle (p &lt; 0.05)and blood lactate (p &lt; 0.05)were observed following BFRT intervention compared to BFRT + WBV intervention.

Conclusion: For sprint performance, BFRT and WBV had similar post-activation enhancement effects to BFRT + WBV, and the metabolic accumulation immediately following the BFRT were higher than that following BFRT + WBV in male sprinters.

Effects of Low-Load Blood Flow Restriction Resistance Training on Muscle Strength and Hypertrophy Compared with Traditional Resistance Training in Healthy Adults Older Than 60 Years: Systematic Review and Meta-Analysis

BACKGROUND

There is clinical interest in determining the effects of low-load blood flow restriction (LL-BFR) resistance training on muscle strength and hypertrophy compared with traditional high- and low-load (HL and LL) resistance training in healthy older adults and the influence of LL-BFR training cuff-pressure on these outcomes.

METHODS

A search was performed on the MEDLINE, PEDro, CINHAL, Web of Science, Science Direct, Scopus, and CENTRAL databases.

RESULTS

The analysis included 14 studies. HL resistance training produces a small increase in muscle strength (eight studies; SMD, -0.23 [-0.41; -0.05]) but not in muscle hypertrophy (six studies; (SMD, 0.08 [-0.22; 0.38]) when compared with LL-BFR resistance training. Compared with traditional LL resistance training, LL-BFR resistance training produces small-moderate increases in muscle strength (seven studies; SMD, 0.44 [0.28; 0.60]) and hypertrophy (two studies; SMD, 0.51 [0.06; 0.96]). There were greater improvements in muscle strength when higher cuff pressures were applied versus traditional LL resistance training but not versus HL resistance training.

CONCLUSIONS

LL-BFR resistance training results in lower muscle strength gains than HL resistance training and greater than traditional LL resistance training in healthy adults older than 60 years. LL-BFR resistance training promotes a similar muscle hypertrophy to HL resistance training but is greater than that of traditional LL resistance training. Applying cuff pressures above the limb occlusion pressure could enhance the increases in muscle strength compared with traditional LL resistance training.

Acute Responses to Cycling Exercise With Blood Flow Restriction During Various Intensities

ABSTRACT

Lauver, JD, Moran, A, Guilkey, JP, Johnson, KE, Zanchi, NE, and Rotarius, TR. Acute responses to cycling exercise with blood flow restriction during various intensities. J Strength Cond Res 36(12): 3366-3373, 2022-The purpose of this study was to investigate the acute physiological responses during cycling at various intensities with blood flow restriction (BFR). Subjects ( N = 9; V̇ o2 peak = 36.09 ± 5.80 ml·kg -1 ·min -1 ) performed 5 protocols: high-intensity (HIGH), control (CON-90), 90% of ventilatory threshold (VT) work rate with BFR (90-BFR), 70% of VT with BFR (70-BFR), and 30% V̇ o2 peak with BFR (30-BFR). Protocols consisted of five 2-minute work intervals interspersed with 1-minute recovery intervals. Blood flow restriction pressure was 80% of limb occlusion pressure. V̇ o2 , muscle excitation, tissue oxygen saturation (StO 2 ), discomfort, and level of perceived exertion (RPE) were assessed. Muscle excitation was higher during HIGH (302.9 ± 159.9 %BSL [baseline]) compared with 70-BFR (99.7 ± 76.4 %BSL) and 30-BFR (98.2 ± 70.5 %BSL). StO 2 was greater during 90-BFR (40.7 ± 12.5 ∆BSL), 70-BFR (34.4 ± 15.2 ∆BSL), and 30-BFR (31.9 ± 18.7 ∆BSL) compared with CON-90 (4.4 ± 11.5 ∆BSL). 90-BFR (39.6 ± 12.0 ∆BSL) resulted in a greater StO 2 -Avg compared with HIGH (20.5 ± 13.8 ∆BSL). Also, HIGH (23.68 ± 5.31 ml·kg -1 ·min -1 ) resulted in a greater V̇ o2 compared with 30-BFR (15.43 ± 3.19 ml·kg -1 ·min -1 ), 70-BFR (16.65 ± 3.26 ml·kg -1 ·min -1 ), and 90-BFR (18.28 ± 3.89 ml·kg -1 ·min -1 ); 90-BFR (intervals: 4 = 15.9 ± 2.3; intervals: 5 = 16.4 ± 2.5) resulted in a greater RPE compared with 30-BFR (intervals: 4 = 13.3 ± 1.4; intervals: 5 = 13.7 ± 1.7) during intervals 4 and 5. These results suggest that when adding BFR to various intensities of aerobic exercise, consideration should be given to peak work and VT to provide a balance between high local physiological stress and perceptual responses.

Effects of Low Intensity Blood Flow Restriction Training on Muscle Volume, Strength and Power in Healthy Middle-Aged Females

OBJECTIVES The purpose of this study is to investigate the efficacy of weight training with controlled blood flow occlusion compared to conventional resistance training, in the ageing population.METHODS Twenty-three healthy female subjects (aged 40-55) were randomly assigned to one of three groups; low intensity blood flow restriction training (LI-BFRT) (n = 9), conventional resistance training (RT) (n = 7) and control (CON) (n = 7). The RT group trained between 65-70% one repetition maximum (1RM) and the LI-BFRT group trained at 30% 1RM while wearing pressure cuffs inflated to 100-120% of brachial systolic blood pressure (bSBP). Relative appendicular skeletal muscle mass (ASM/weight), isokinetic strength and power were tested pre and post 8 weeks of training.RESULTS Upper limb ASM/weight increased significantly in the LI-BFRT and RT groups (both p < 0.001). Only LI-BFRT showed significant difference compared with the CON group (p < 0.01). Lower limb ASM/weight improved in both the LI-BFRT (p < 0.01) and CON (p < 0.01) groups without group differences. Lower limb flexion strength increased in the LI-BFRT and RT groups (both p < 0.01), with differences between groups (p < 0.01, LI-BFRT > RT > CON). Only RT increased extension muscle strength (p < 0.05). Lower limb flexion and extension power improved following LI-BFRT (p < 0.05 and p < 0.01, respectively), significantly greater than RT in both flexion (p < 0.001) and extension (p < 0.01).CONCLUSIONS LI-BFRT may be as, if not more effective than RT for increasing muscle volume, strength and power in middle-aged women.

Running Training Combined With Blood Flow Restriction Increases Cardiopulmonary Function and Muscle Strength in Endurance Athletes

ABSTRACT

Chen, Y-T, Hsieh, Y-Y, Ho, J-Y, Lin, T-Y, and Lin, J-C. Running training combined with blood flow restriction increases cardiopulmonary function and muscle strength in endurance athletes . J Strength Cond Res 36(5): 1228-1237, 2022-We investigated the effects of 8 weeks (3 d/wk) of running training (RT) combined with blood flow restriction (RT-BFR) on cardiopulmonary function and muscle strength in endurance athletes. Twenty endurance-trained male athletes (19-25 years; 177.6 ± 2.4 cm; 69.0 ± 2.2 kg) were pair matched and randomly assigned to RT-BFR and RT groups. The RT-BFR group performed running sessions (50% heart rate reserve; 3-minute × 5 sets; 1-minute rest interval) with pressure cuffs (1.3 × resting systolic blood pressure), whereas the RT group performed the same running sessions without pressure cuffs. V̇o2max, muscle mass, isokinetic muscle strength, and hormones were assessed at pre-, mid- and posttraining. Compared with the RT group, the RT-BFR group exhibited a significantly greater increase in V̇o2max (5.1 vs. -1.1%) and isokinetic knee extensor strength (16.5 vs. -5.9%). In addition, RT-BFR group presented higher leg muscle mass (10.3 vs. 9.7 kg) than that of RT group after 8 weeks of training. Furthermore, testosterone to cortisol (T:C) ratio at 24 hours after training session at pre-, mid-, and posttraining were maintained in the RT-BFR group, whereas significant decreases of T:C ratio at 24 hours after training session were observed in the RT group. These results suggested that RT combined with BFR may be a practical training strategy for promoting cardiopulmonary function and muscle strength in endurance runners.

Aerobic exercise with blood flow restriction: energy expenditure, excess post-exercise oxygen consumption, and respiratory exchange ratio

We compared the effects of aerobic exercise with and without blood flow restriction (BFR) to high-intensity aerobic exercise on energy expenditure (EE), excess post-exercise oxygen consumption (EPOC), and respiratory exchange ratio (RER) during and after exercise. Twenty-two recreationally active males randomly completed the following experimental conditions: AE - aerobic exercise without BFR, AE+BFR - aerobic exercise with BFR, HIAE - high-intensity aerobic exercise, CON - non-exercise control condition. EE was significantly (p<0.05) greater during exercise for HIAE compared to all conditions, and for AE+BFR compared to AE and CON during and post-exercise exercise. There were no significant (p>0.05) differences in EPOC between HIAE and AE+BFR at any time point, however, both conditions were significantly (p < 0.05) greater than the AE (d = 1.50 and d = 1.03, respectively) and CON at the first 10 minutes post-exercise. RER during exercise for HIAE was significantly (p<0.05) greater than AE+BFR at the first 6 minutes of exercise (p = 0.003, d = 0.88), however, no significant differences were observed from 9 min up to the end of the exercise. HIAE was also significantly (p<0.05) greater than AE and CON at all time points during exercise, whereas, AE+BFR was significantly (p<0.05) greater than CON at all time points but not significantly (p < 0.05) different than AE (p<0.05); although the overall session RER was significantly (p<0.05) greater during AE+BFR than AE. Altogether, continuous AE+BFR results in greater EE compared to volume matched AE, as well as a similar EPOC compared to HIAE. This article is protected by copyright. All rights reserved.

Optimization of Exercise Countermeasures to Spaceflight Using Blood Flow Restriction

INTRODUCTION: During spaceflight missions, astronauts work in an extreme environment with several hazards to physical health and performance. Exposure to microgravity results in remarkable deconditioning of several physiological systems, leading to impaired physical condition and human performance, posing a major risk to overall mission success and crew safety. Physical exercise is the cornerstone of strategies to mitigate physical deconditioning during spaceflight. Decades of research have enabled development of more optimal exercise strategies and equipment onboard the International Space Station. However, the effects of microgravity cannot be completely ameliorated with current exercise countermeasures. Moreover, future spaceflight missions deeper into space require a new generation of spacecraft, which will place yet more constraints on the use of exercise by limiting the amount, size, and weight of exercise equipment and the time available for exercise. Space agencies are exploring ways to optimize exercise countermeasures for spaceflight, specifically exercise strategies that are more efficient, require less equipment, and are less time-consuming. Blood flow restriction exercise is a low intensity exercise strategy that requires minimal equipment and can elicit positive training benefits across multiple physiological systems. This method of exercise training has potential as a strategy to optimize exercise countermeasures during spaceflight and reconditioning in terrestrial and partial gravity environments. The possible applications of blood flow restriction exercise during spaceflight are discussed herein.Hughes L, Hackney KJ, Patterson SD. Optimization of exercise countermeasures to spaceflight using blood flow restriction. Aerosp Med Hum Perform. 2021; 93(1):32-45.

Blood Flow Restriction Enhances Rehabilitation and Return to Sport: The Paradox of Proximal Performance

The use of blood flow restriction (BFR) within rehabilitation is rapidly increasing as further research is performed elucidating purported benefits such as improved muscular strength and size, neuromuscular control, decreased pain, and increased bone mineral density. Interestingly, these benefits are not isolated to structures distal to the occlusive stimulus. Proximal gains are of high interest to rehabilitation professionals, especially those working with patients who are limited due to pain or postsurgical precautions. The review to follow will focus on current evidence and ongoing hypotheses regarding physiologic responses to BFR, current clinical applications, proximal responses to BFR training, potential practical applications for rehabilitation and injury prevention, and directions for future research. Interestingly, benefits have been found in musculature proximal to the occlusive stimulus, which may lend promise to a greater variety of patient populations and conditions. Furthermore, an increasing demand for BFR use in the sports world warrants further research for performance research and recovery.

LEVEL OF EVIDENCE

Level V, expert opinion.

The Evolution of Blood Flow Restricted Exercise

The use of blood flow restricted (BFR) exercise has become an accepted alternative approach to improve skeletal muscle mass and function and improve cardiovascular function in individuals that are not able to or do not wish to use traditional exercise protocols that rely on heavy loads and high training volumes. BFR exercise involves the reduction of blood flow to working skeletal muscle by applying a flexible cuff to the most proximal portions of a person’s arms or legs that results in decreased arterial flow to the exercising muscle and occluded venous return back to the central circulation. Safety concerns, especially related to the cardiovascular system, have not been consistently reported with a few exceptions; however, most researchers agree that BFR exercise can be a relatively safe technique for most people that are free from serious cardiovascular disease, as well as those with coronary artery disease, and also for people suffering from chronic conditions, such as multiple sclerosis, Parkinson’s, and osteoarthritis. Potential mechanisms to explain the benefits of BFR exercise are still mostly speculative and may require more invasive studies or the use of animal models to fully explore mechanisms of adaptation. The setting of absolute resistive pressures has evolved, from being based on an individual’s systolic blood pressure to a relative measure that is based on various percentages of the pressures needed to totally occlude blood flow in the exercising limb. However, since several other issues remain unresolved, such as the actual external loads used in combination with BFR, the type of cuff used to induce the blood flow restriction, and whether the restriction is continuous or intermittent, this paper will attempt to address these additional concerns.

Acute Effects of Local Ischemic Hypoxia and Systemic Hypoxemia on Neuromuscular and Cognitive Function

Rivera, Paola M., Chris E. Proppe, Esther Beltran, and Ethan C. Hill. Acute effects of local ischemic hypoxia and systemic hypoxemia on neuromuscular and cognitive function. High Alt Med Biol. 00:000-000, 2021. Background: The application of blood flow restriction (BFR) induces local ischemic hypoxia within the muscle(s) distal to the restriction device. Systemic hypoxemia via oxygen or barometric pressure manipulation achieves whole-body hypoxia and thus may be a more potent exercise adjunct than BFR. Therefore, the purpose of this study was to examine the acute effects of local ischemic hypoxia versus systemic hypoxemia on maximal voluntary isometric contraction (MVIC) torque, electromyographic amplitude (EMG AMP), EMG mean power frequency (MPF), and cognition. Materials and Methods: Twelve recreationally trained women (mean age ± standard deviation = 21 ± 1.6 years) performed 75 submaximal (1 × 30, 3 × 15) unilateral leg extension muscle actions under normoxia, local ischemic hypoxia, and systemic hypoxemia. Before and immediately after the 75 repetitions, MVIC muscle actions were performed, and surface EMG was simultaneously assessed from the vastus lateralis. Cognitive function was assessed immediately after each exercise using the Automated Neuropsychological Assessment Metrics (ANAM). Separate repeated-measures analyses of variance (ANOVAs) were performed to examine changes in MVIC, reaction time, EMG AMP, and EMG MPF responses during the MVIC muscle actions. Results: There were no significant (p = 0.21-0.953) Condition × Time interactions for MVIC, EMG AMP, or EMG MPF but a significant (p < 0.001-0.005) main effect for the Time collapsed across Condition for MVIC torque (pretest 238.8 ± 19.5, posttest 212.7 ± 20.1 Nm) and EMG MPF (88.5% ± 1.4% of pretest). There were no significant (p = 0.503) differences in reaction time among Conditions. Conclusions: The findings of the present study suggest that all three conditions elicited comparable acute changes in performance as assessed by MVIC torque that were associated with no changes in muscle activation but decrease in action potential conduction velocity. Therefore, the application of local ischemic hypoxia or systemic hypoxemia during low-load resistance exercise can be used to elicit similar acute physiological responses and not adversely affect cognitive function relative to nonhypoxic conditions.

The Effect of Body Position and the Reliability of Upper Limb Arterial Occlusion Pressure Using a Handheld Doppler Ultrasound for Blood Flow Restriction Training

BACKGROUND

The precise calculation of arterial occlusive pressure is essential to accurately prescribe individualized pressures during blood flow restriction training. Arterial occlusion pressure in the lower limb varies significantly between different body positions while similar reports for the upper limb are lacking.

HYPOTHESIS

Body position has a significant effect in upper limb arterial occlusive pressure. Using cuffs with manual pump and a handheld Doppler ultrasound can be a reliable method to determine upper limb arterial blood flow restriction.

STUDY DESIGN

A randomized repeated measures design.

LEVEL OF EVIDENCE

Level 3.

METHODS

Forty-two healthy participants (age mean ± SD = 28.1 ± 7.7 years) completed measurements in supine, seated, and standing position by 3 blinded raters. A cuff with a manual pump and a handheld acoustic ultrasound were used. The Wilcoxon signed-rank test with Bonferroni correction was used to analyze differences between body positions. A within-subject coefficient of variation and an intraclass correlation coefficient (ICC) test were used to calculate reproducibility and reliability, respectively.

RESULTS

A significantly higher upper limb arterial occlusive pressure was found in seated compared with supine position (P < 0.031) and in supine compared with standing position (P < 0.031) in all raters. An ICC of 0.894 (95% CI = 0.824-0.939, P < 0.001) was found in supine, 0.973 (95% CI = 0.955-0.985, P < 0.001) in seated, and 0.984 (95% CI = 0.973-0.991, P < 0.001) in standing position. ICC for test-retest reliability was found 0.90 (95% CI = 0.814-0.946, P < 0.001), 0.873 (95% CI = 0.762-0.93, P < 0.001), and 0.858 (95% CI = 0.737-0.923, P < 0.001) in the supine, seated, and standing position, respectively.

CONCLUSION

Upper limb arterial occlusive pressure was significantly dependent on body position. The method showed excellent interrater reliability and repeatability between different days.

CLINICAL RELEVANCE

Prescription of individualized pressures during blood flow restriction training requires measurement of upper limb arterial occlusive pressure in the appropriate position. The use of occlusion cuffs with a manual pump and a handheld Doppler ultrasound showed excellent reliability; however, the increased measurement error compared with the differences in arterial occlusive pressure between certain positions should be carefully considered for the clinical application of the method.

STRENGTH OF RECOMMENDATIONS TAXONOMY (SORT)

B.

Acute physiological and perceptual responses to moderate intensity cycling with different levels of blood flow restriction

The aim of this study was to compare: i) the physiological and perceptual responses of low-load exercise [(moderate intensity exercise (MI)] with different levels of blood flow restriction (BFR), and ii) MI with BFR on the bike with high intensity (HI) exercise without BFR. The protocol involved large muscle mass exercise at different levels of BFR, and this differentiates our study from others. Twenty-one moderately trained males (age: 24.6 ± 2.4 years; VO_2peak: 47.2 ± 7.0 ml^.kg^-1.min^-1, mean ± sd) performed one maximal graded exercise test and seven 5-min constant-load cycling bouts. Six bouts were at MI [40% _peak power (P_peak), 60%VO_2peak], one without BFR and five with different levels of BFR (40%, 50%, 60%, 70%, 80% of estimated arterial occlusion pressure). The HI bout (70%P_peak, 90%VO_2peak) was without BFR. Oxygen uptake (VO₂), heart rate (HR), blood lactate (BLa), rate of perceived exertion (RPE), and tissue oxygen saturation (TSI) were recorded. Regardless of pressure, HR, BLa and RPE during MI-BFR were higher compared to MI (p < 0.05, ES: moderate to very large), and TSI reduction was greater in MI-BFR than MI (p < 0.05, ES: moderate to large). The responses of VO₂, HR, BLa, RPE and TSI induced by the different levels of BFR in MI-BFR were similar. Regardless of pressure, the responses of VO₂, HR, BLa and RPE induced by MI-BFR were lower than HI (p < 0.05), except for TSI. TSI change was similar between MI-BFR and HI. It appears that BFR equal to 40% of arterial occlusion pressure is sufficient to reduce TSI when exercising with a large muscle mass.

Is blood flow-restricted training effective for rehabilitation of a pianist with residual neurological symptoms in the upper limbs? A case study

[Purpose] We investigated whether blood flow-restricted training known as KAATSU training, was effective for rehabilitation of a pianist with residual neurological symptoms in the upper limbs. [Participant and Methods] A pianist with residual neurological symptoms in the upper body played “Revolutionary Etude” under two conditions: piano performance with (Piano-blood flow-restricted) and without (Piano-control) the restriction of blood flow to the upper limbs. In the Piano-blood flow-restricted exercise, a pressure of 130–170 mmHg was applied around the most proximal portion of both arms. The changes in upper limb circumference and muscle strength were measured before, immediately after, and 15 min after the performance. The impression of the piano performance was recorded after the Piano-blood flow-restricted exercise. [Results] Immediately after the piano performance, the forearm and upper arm circumferences had increased significantly in both arms, and the change was greater in the Piano-blood flow-restricted than in the Piano-control condition. The handgrip strength for the right arm also showed greater changes in the former than the latter. However, there were no significant differences between the two conditions regarding the handgrip strength of the left arm. [Conclusion] There is a high possibility that blood flow-restricted training is effective for rehabilitation of the pianist with residual neurological symptoms in the upper limbs.

Unilateral, bilateral, and alternating muscle actions elicit similar muscular responses during low load blood flow restriction exercise

PURPOSE

Compare acute muscular responses to unilateral, bilateral, and alternating blood flow restriction (BFR) exercise.

METHODS

Maximal strength was tested on visit one. On visits 2-4, 2-10 days apart, 19 participants completed 4 sets of knee extensions (30% one-repetition maximum) with BFR (40% arterial occlusion pressure) to momentary failure (inability to lift load) using each muscle action (counterbalanced order). Ultrasound muscle thickness was measured at 60% and 70% of the anterior thigh before (Pre), immediately (Post-0), and 5 min (Post-5) after exercise. Surface electromyography and tissue deoxygenation were measured throughout. Results, presented as means, were analyzed with a three-way (sex by time by condition) Bayesian RMANOVA.

RESULTS

There was a time by sex interaction (BF_inclusion: 5.489) for left leg 60% muscle thickness (cm). However, changes from Pre to Post-0 (males: 0.39 vs females: 0.26; BF₁₀: 0.839), Post-0 to Post-5 (males: - 0.05 vs females: - 0.06; BF₁₀: 0.456), and Pre to Post-5 (males: 0.34 vs females: 0.20; BF₁₀: 0.935) did not differ across sex. For electromyography (%MVC), there was a sex by condition interaction (BF_inclusion: 550.472) with alternating having higher muscle excitation for females (16) than males (9; BF₁₀: 5.097). Tissue deoxygenation (e.g. channel 1, µM) increased more for males (sets 1: 11.17; 2: 2.91; 3: 3.69; 4: 3.38) than females (sets 1: 4.49; 2: 0.24; 3: - 0.10; 4: - 0.06) from beginning to end of sets (all BF_inclusion ≥ 4.295e + 7). For repetitions, there was an interaction (BF_inclusion: 17.533), with alternating completing more than bilateral and unilateral for set one (100; 56; 50, respectively) and two (34; 16; 18, respectively).

CONCLUSION

Alternating, bilateral, and unilateral BFR exercise elicit similar acute muscular responses.

The effect of muscle blood flow restriction on hemodynamics, cerebral oxygenation and activation at rest

This study tested the hypothesis that muscle blood flow restriction reduces muscle and cerebral oxygenation, at rest. In 26 healthy males, aged 33±2 yrs, physiological variables were continuously recorded during a 10-min period in two experimental conditions: a) with muscle blood flow restriction through thigh cuffs application inflated at 120 mmHg (With Cuffs, WC) and b) without restriction (No Cuffs, NC). Muscle and cerebral oxygenation were reduced by muscle blood flow restriction as suggested by the increase in both muscle and cerebral deoxygenated hemoglobin (Δ[HHb]; p<0.01) and the decrease of muscle and cerebral oxygenation index (Δ[HbDiff]; p<0.01). Hemodynamic responses were not affected by such muscle blood flow restriction, whereas baroreflex sensitivity was reduced (p=0.009). The perception of leg discomfort was higher (p<0.001) in the WC than in the NC condition. This study suggests that thigh cuffs application inflated at 120 mmHg is an effective method to reduce muscle oxygenation at rest. These changes at the muscular level seem to be sensed by the central nervous system, evoking alterations in cerebral oxygenation and baroreflex sensitivity. Novelty bullets: • Thigh cuffs application inflated at 120 mmHg effectively reduces muscle oxygenation at rest. • Limiting muscle oxygenation appears to reduce cerebral oxygenation, and baroreflex sensitivity, at rest. • Even in healthy subjects, limiting muscle oxygenation, at rest, affects neural integration.

Effects of Blood Flow Restriction Training on Muscle Strength and Pain in Patients With Knee Injuries: A Meta-Analysis

BACKGROUND

Due to the pain caused by knee injuries, low-load resistance training with blood flow restriction (L-BFR) may be a potential adjuvant therapeutic tool in the rehabilitation of knee injuries. This review aimed to analyze the effectiveness of L-BFR training modality in knee rehabilitation.

DESIGN

A meta-analysis was conducted to determine the potential impact of blood flow restriction on patients with knee injuries. PubMed, EBSCO, and Web of Science databases were searched for eligible studies from January 2000 until January 2020. The mean differences of the data were analyzed using Revman 5.3 software with a 95% confidence interval.

RESULTS

Nine studies fulfilled the inclusion criteria. These studies involved 179 patients who received L-BFR, 96 patients who underwent high-load resistance training, and another 94 patients who underwent low-load resistance training. The analysis of pooled data showed that patients in both the L-BFR (standardized mean difference, 0.83 [0.53, 1.14], P < 0.01) and high-load resistance training (standardized mean difference, -0.09 [-0.43, 0.24], P = 0.58) groups experienced an increase in muscle strength after the training. In addition, pain score was significantly reduced in the L-BFR group compared with the other two groups (standardized mean difference, -0.61 [-1.19, -0.03], P = 0.04).

CONCLUSIONS

Muscle strength increased after L-BFR and high-load resistance training compared with low-load resistance training. Furthermore, pain score was significantly reduced after L-BFR. Hence, L-BFR is a potential intervention to be applied in rehabilitation of knee injuries.

Isometric blood flow restriction exercise: acute physiological and neuromuscular responses

Background

Numerous studies have demonstrated that the addition of blood flow restriction (BFR) to low-load (LL) resistance exercise leads to elevated levels of muscle hypertrophy and strength gains. In terms of main underlying mechanisms, metabolic accumulation and increased neuromuscular adaptations seem to play a primary role. However, this evidence is largely based on dynamic exercise conditions. Therefore, the main objective was to investigate the acute physiological adaptations following isometric LL-BFR exercise.

Methods

Fifteen males participated in this cross-over trial and completed the following sessions in a random and counterbalanced order: isometric LL-BFR exercise (20% maximum voluntary contraction, MVC) and load matched LL exercise without BFR. Lactate levels, muscle activation as well as muscle swelling were recorded during the whole exercise and until 15 min post completion. Additionally, changes in maximal voluntary torque and ratings of perceived exertion (RPE) were monitored.

Results

During exercise, EMG amplitudes (72.5 ± 12.7% vs. 46.3 ± 6.7% of maximal EMG activity), muscle swelling and RPE were significantly higher during LL-BFR compared to LL (p < 0.05). Lactate levels did not show significant group differences during exercise but revealed higher increases 15 min after completion in the LL-BFR condition (LL-BFR: + 69%, LL: + 22%) (p < 0.05). Additionally, MVC torque significantly decreased immediately post exercise only in LL-BFR (~ − 11%) (p < 0.05) but recovered after 15 min.

Conclusions

The present results demonstrate that isometric LL-BFR causes increased metabolic, neuromuscular as well as perceptual responses compared to LL alone. These adaptations are similar to dynamic exercise and therefore LL-BFR represents a valuable type of exercise where large joint movements are contraindicated (e.g. rehabilitation after orthopedic injuries).

The perceptual responses of individuals with multiple sclerosis to blood flow restriction versus traditional resistance exercise

BACKGROUND

Low-load resistance exercise with blood flow restriction (_LLBFR-RE) has been shown capable of improving neuromuscular parameters in several clinical populations, however, its tolerability and effects on individuals with multiple sclerosis (MS) remains unknown.

OBJECTIVE

To investigate the perceptual responses of individuals with MS to _LLBFR-RE versus traditional high-load resistance exercise (HL-RE).

METHODS

Four men and eleven women diagnosed with relapsing-remitting MS randomly completed the following experimental trials: 1) _LLBFR-RE four sets of 30-15-15-15 repetitions, at 20% of one-repetition maximum (1-RM) of leg-press (LP) and knee-extension (KE), with 50% of BFR, and a 1-min rest interval between sets; 2) HL-RE- four sets of 8-10 repetitions, at 70% 1-RM of LP and KE, with the same rest intervals. Ratings of perceived exertion (RPE) were measured after each set, pain was measured before and after sets, and delayed-onset muscle soreness (DOMS) was measured at 5, 30, 60 min, and 24-h post-exercise.

RESULTS

HL-RE elicited significantly (p<0.05) greater RPE compared to _LLBFR-RE during all sets. Additionally, there were no significant (p>0.05) differences between _LLBFR-RE and HL-RE for pain immediately after all sets, although pain measured before sets were significantly (p<0.05) greater for _LLBFR-RE. Finally, both protocols resulted in similar DOMS, however, it was significantly (p<0.05) elevated 24-h post-exercise compared to 1-h after for HL-RE but not for _LLBFR-RE.

CONCLUSION

Altogether, these data demonstrate that _LLBFR-RE is well tolerated by individuals with MS, requires less muscular exertion than HL-RE, and does not cause exaggerated pain during exercise or elevated DOMS up to 24 h post-exercise.

Acute Effects of Interset Rest Duration on Physiological and Perceptual Responses to Resistance Exercise in Hypoxia

Lockhart, C, Scott, BR, Thoseby, B, and Dascombe, BJ. Acute effects of interset rest duration on physiological and perceptual responses to resistance exercise in hypoxia. J Strength Cond Res 34(8): 2241-2249, 2020-This study aimed to determine whether manipulating interset rest periods during resistance training in hypoxia impacts on physiological and perceptual responses to exercise. Twelve healthy males completed 1 repetition maximum (1RM) testing for the bilateral leg extension, before completing 4 separate randomized trials comprising 5 × 10 repetitions of leg extensions at 70% 1RM. Experimental trials were completed in both moderate hypoxia (FIO2 = 15%) and normoxia (FIO2 = 21%), using interset rest periods of both 60 and 180 seconds for each environmental condition. Near-infrared spectroscopy was used to quantify muscle oxygenation of vastus lateralis , and surface electromyography assessed the activation of vastus lateralis and medialis. Blood lactate concentration ([BLa]) and midthigh circumference were assessed before and immediately after each trial. Heart rate (HR) responses, blood oxygen saturation, and rating of perceived exertion (RPE) were also assessed after each set and the whole session RPE (sRPE). Perceived quadriceps soreness was reported before, immediately after, and at 24 and 48 hours after each trial. Muscle activation (sets 4-5), RPE (sets 3-5), and sRPE were significantly (p < 0.05) higher in the 60-second trials of the resistance exercise protocol. Significant increases (p < 0.01) were observed for [BLa] and midthigh circumference across sets within each condition. No significant main effect was observed for interset rest duration or environmental condition for muscle oxygenation, HR, or perceived quadriceps soreness. These findings indicate that performing resistance exercise in hypoxia or normoxia with shortened interset rest periods increases muscle activation and perceived exertion, without exacerbating muscle soreness.

Effect of prehabilitation in older adults undergoing total joint replacement: An Overview of Systematic Reviews

Purpose of Review

To review and discuss the findings of systematic reviews that synthesized the evidence on the effect of preoperative exercises (prehabilitation) on postoperative functional recovery in older adults undergoing total knee or hip joint replacement.

Recent Findings

Ten systematic reviews (8 meta-analyses) were included in this review. Findings from the systematic reviews indicated that prehabilitation decreases length of hospital stay but does not improve postoperative functional recovery in older adults undergoing joint replacement. Individual studies in the systematic reviews varied considerably in prehabilitation protocol, assessment timepoints, and outcome measures. Most importantly, systematic reviews did not assess the outcomes pre-post prehabilitation as this timepoint was not addressed in most individual studies. Therefore, it is not known whether the prehabilitation programs improved outcomes preoperatively.

Summary

There is a need to develop comprehensive prehabilitation protocols and systematically assess the preoperative and postoperative effectiveness of prehabilitation protocols on functional outcomes (i.e., self-reported and performance-based) in older adults undergoing total joint replacement.

Perceptual and Neuromuscular Responses Adapt Similarly Between High-Load Resistance Training and Low-Load Resistance Training With Blood Flow Restriction

Teixeira, EL, Painelli, VdS, Schoenfeld, BJ, Silva-Batista, C, Longo, AR, Aihara, AY, Cardoso, FN, Peres, BdA, and Tricoli, V. Perceptual and neuromuscular responses adapt similarly between high-load resistance training and low-load resistance training with blood flow restriction. J Strength Cond Res XX(X): 000-000, 2020-This study compared the effects of 8 weeks of low-load resistance training with blood flow restriction (LL-BFR) and high-load resistance training (HL-RT) on perceptual responses (rating of perceived exertion [RPE] and pain), quadriceps cross-sectional area (QCSA), and muscle strength (1 repetition maximum [RM]). Sixteen physically active men trained twice per week, for 8 weeks. One leg performed LL-BFR (3 sets of 15 repetitions, 20% 1RM), whereas the contralateral leg performed HL-RT (3 sets of 8 repetitions, 70% 1RM). Rating of perceived exertion and pain were evaluated immediately after the first and last training sessions, whereas QCSA and 1RM were assessed at baseline and after training. Rating of perceived exertion was significantly lower (6.8 ± 1.1 vs. 8.1 ± 0.8, p = 0.001) and pain significantly higher (7.1 ± 1.2 vs. 5.8 ± 1.8, p = 0.02) for LL-BFR than that for HL-RT before training. Significant reductions in RPE and pain were shown for both protocols after training (both p < 0.0001), although no between-protocol differences were shown in absolute changes (p = 0.10 and p = 0.48, respectively). Both LL-BFR and HL-RT were similarly effective in increasing QCSA (7.0 ± 3.8% and 6.3 ± 4.1%, respectively; both p < 0.0001) and 1RM (6.9 ± 4.1% and 13.7 ± 5.9%, respectively; both P < 0.0001), although absolute changes for 1RM in HL-RT were greater than LL-BFR (p = 0.001). In conclusion, LL-BFR produces lower RPE values and a higher pain perception than HL-RT. However, consistent application of these approaches result in chronic adaptations so that there are no differences in perceptual responses over the course of time. In addition, muscle strength is optimized with HL-RT despite similar increases in muscle hypertrophy between conditions.

A Systematic Review and Meta-Analysis on Neural Adaptations Following Blood Flow Restriction Training: What We Know and What We Don't Know

Objective: To summarize the existing evidence on the long-term effects of low-load (LL) blood flow restricted (BFR) exercise on neural markers including both central and peripheral adaptations. Methods: A systematic review and meta-analysis was conducted according to the PRISMA guidelines. The literature search was performed independently by two reviewers in the following electronic databases: PubMed, Web of Science, Scopus and CENTRAL. The systematic review included long-term trials investigating the effects of LL-BFR training in healthy subjects and compared theses effects to either LL or high-load (HL) training without blood flow restriction. Results: From a total of N = 4499 studies, N = 10 studies were included in the qualitative synthesis and N = 4 studies in a meta-analysis. The findings indicated that LL-BFR resulted in enhanced levels of muscle excitation compared to LL training with pooled effect sizes of 0.87 (95% CI: 0.38-1.36). Compared to HL training, muscle excitation following LL-BFR was reported as either similar or slightly lower. Differences between central activation between LL-BFR and LL or HL are less clear. Conclusion: The summarized effects in this systematic review and meta-analysis highlight that BFR training facilitates neural adaptations following LL training, although differences to conventional HL training are less evident. Future research is urgently needed to identify neural alterations following long-term blood flow restricted exercise.

Acute cardiovascular response to unilateral, bilateral, and alternating resistance exercise with blood flow restriction

AIM

Blood flow restriction (BFR) exercise is a common alternative to traditional high-load resistance exercise used to increase muscle size and strength. Some populations utilizing BFR at a low load may wish to limit their cardiovascular response to exercise. Different contraction patterns may attenuate the cardiovascular response, but this has not been compared using BFR.

PURPOSE

To compare the cardiovascular response to unilateral (UNI), bilateral (BIL), and alternating (ALT) BFR exercise contraction patterns.

METHODS

Twenty healthy participants performed four sets (30 s rest) of knee extensions to failure, using 30% one-repetition maximum, 40% arterial occlusion pressure, and each of the three contraction patterns (on different days, at the same time of day, separated by 2-10 days, randomized). Cardiovascular responses, presented as pre- to post-exercise mean changes (SD), were measured using pulse wave analysis and analyzed with Bayesian RMANOVA.

RESULTS

ALT caused greater changes in: aortic systolic [ΔmmHg: ALT = 21(8); UNI = 13(11); BIL = 15(8); BF₁₀ = 29.599], diastolic [ΔmmHg: ALT = 13(8); UNI = 7(11); BIL = 8(8); BF₁₀ = 5.175], and mean arterial [ΔmmHg: ALT = 19(8); UNI = 11(11); BIL = 13(7); BF₁₀ = 48.637] blood pressures. Aortic [ΔmmHg bpm: ALT = 4945(2340); UNI = 3294(1408); BIL = 3428 (1461); BF₁₀ = 113.659] and brachial [ΔmmHg bpm: ALT = 6134(2761); UNI = 4300(1709); BIL = 4487(1701); BF₁₀ = 31.845] rate pressure products, as well as heart rate [Δbpm: ALT = 26(14); UNI = 19(8); BIL = 19(11); BF₁₀ = 5.829] were greatest with ALT. Augmentation index [Δ%: UNI = -6(13); BIL = - 7(11); ALT = - 5(16); BF₁₀ = 0.155] and wave reflection magnitude [Δ%: UNI = - 5(9); BIL = - 4(7); ALT = - 4(7); BF₁₀ = 0.150] were not different.

CONCLUSION

Those at risk of a cardiovascular event may choose unilateral or bilateral BFR exercise over alternating until further work determines the degree to which it can be tolerated.

Acute physiological responses to combined blood flow restriction and low-level laser

PURPOSE

Blood flow restriction (BFR) is an innovation in fitness to train muscles with low loads at low oxygen levels. Low-level laser therapy (LLLT) is a bio-energetic approach to alleviate muscle fatigue during resistance training. This study investigated the immediate effect of LLLT pre-conditioning on BFR that accelerates muscle fatigue due to ischemia.

METHODS

Fifteen young adults participated in this study of a crossover randomized design. They completed a low-load contraction with various pre-conditioning (blood flow restriction with low-level laser therapy (LLLT + BFR), blood flow restriction with sham low-level laser therapy (BFR), and control). Force fluctuation dynamics, muscle oxygen saturation of hemoglobin and myoglobin (SmO₂), and discharge patterns of motor units (MU) were compared.

RESULTS

Normalized SmO₂ during low-load contractions significantly varied with the pre-contraction protocols (Control (83.6 ± 3.0%) > LLLT + BFR (70.3 ± 2.8%) > BFR (55.4 ± 2.4%). Also, force fluctuations and MU discharge varied with the pre-contraction protocols. Multi-scale entropy and mean frequency of force fluctuations were greater in the LLLT + BFR condition (31.95 ± 0.67) than in the BFR condition (29.47 ± 0.73). The mean inter-spike interval of MUs was greater in the LLLT + BFR condition (53.32 ± 2.70 ms) than in the BFR condition (45.04 ± 1.08 ms). In particular, MUs with higher recruitment thresholds exhibited greater LLLT-related discharge complexity (LLLT + BFR (0.201 ± 0.012) > BFR (0.154 ± 0.006)).

CONCLUSIONS

LLLT pre-conditioning can minimize the BFR-related decline in muscle oxygen saturation, leading to force gradation and MU discharge in a cost-effective and complex manner.

Blood Flow Restricted Exercise and Discomfort: A Review

Spitz, RW, Wong, V, Bell, ZW, Viana, RB, Chatakondi, RN, Abe, T, and Loenneke, JP. Blood flow restricted exercise and discomfort: A Review. J Strength Cond Res XX(X): 000-000, 2020-Blood flow restriction exercise involves using a pneumatic cuff or elastic band to restrict arterial inflow into the muscle and block venous return out of the muscle during the exercise bout. The resultant ischemia in conjunction with low-load exercise has shown to be beneficial with increasing muscle size and strength. However, a limitation of using blood flow restriction (BFR) is the accompanying discomfort associated with this type of exercise. Factors that may influence discomfort are applied pressure, width of the cuff, cuff material, sex, and training to failure. The goal of this review was to evaluate the existing literature and elucidate how these factors can be manipulated to reduce discomfort during exercise as well as provide possible directions for future research. Thirty-eight different studies were located investigating BFR and discomfort. It was found that BFR training causes more discomfort than exercise without BFR. However, chronic use of BFR may increase tolerability, but discomfort may still be elevated over traditional non-blood flow restricted exercise. Discomfort can be attenuated by the application of lower applied pressures and stopping short of task failure. Finally, in the upper body, wider cuffs seem to increase ratings of discomfort compared with more narrow cuffs. In conclusion, applying the proper-sized cuff and making the applied pressure relative to both the individual and the cuff applied may attenuate discomfort. Reducing discomfort during exercise may help increase adherence to exercise and rehabilitation programs.

Immune System Modulation in Response to Strength Training With Blood Flow Restriction

Souza, TSP, Pfeiffer, PAS, Pereira, JN, Pereira Neto, EA, Dutra, TS, Mendonça, MGL, and Cirilo-Sousa, MS. Immune system modulation in response to strength training with blood flow restriction. J Strength Cond Res XX(X): 000-000, 2019-This study aimed to compare the strength training with blood flow restriction (ST-BFR) to the multiple-set training at different intensities (30% of 1RM and 75% of 1RM) as for their effect on immunoinflammatory responses (total leukocytes, segmented neutrophils, lymphocytes, monocytes, and lymphocyte subpopulations). It is a randomized experimental study with a repeated measures design with inter and intragroup effects of a strength training session. Eighteen physically active adults aged 20-31 years (26.17 ± 3.7 years), apparently healthy, performed a strength training session with 2 exercises. Six milliliters of blood were collected before the training, immediately after the training, and at 30 minutes and 24 hours after the session to carry out the analyses. The results showed that the strength training could promote modulation (time effect) in the leukocyte count (F = 25.86, p < 0.01, η = 0.74), regardless of the method used. Neutrophils (F = 22.71, p < 0.01, η = 0.60), specifically the TCD4+ lymphocytes (F = 6.33, p < 0.05, η = 0, 3), were the main factors responsible for this variation. Despite the similarity, there were differences between the methods in the modulations of total leukocytes (F = 4.16, p < 0.05, η = 0.36) and neutrophils (F = 4.80, p < 0.05, η = 0.39). In conclusion, compared to the multiple-set training, ST-BFR produces immunoinflammatory responses similar to the low-intensity training and different from the high-intensity training. However, the demargination process of some cells was different depending on the method and intensity used. Nevertheless, these variations are compatible with an appropriate recovery process, because the amplitude and length of the modulation curves of leukocytes, and lymphocyte subpopulations were not compatible with immunosuppression.

Knee extension with blood flow restriction: Impact of cuff pressure on hemodynamics

INTRODUCTION

Blood flow restriction (BFR) exercise has emerged as a method of increasing muscle size and strength with low intensity resistance training. While the cuff pressures used during BFR are typically a percentage of resting arterial occlusion pressure (AOP), the impact these cuff pressures have on blood flow during lower body exercise is unknown.

PURPOSE

To determine how various cuff pressures impact blood flow and tissue perfusion during exercise.

METHODS

Eleven healthy male participants completed four sets of knee extension (30 reps per set at 30% max torque) with 0%, 60%, 80%, and 100% of arterial occlusion pressure (AOP) was applied to the proximal portion of the thigh. Femoral artery blood flow, tissue oxygenation, and central hemodynamics were continuously recorded before, during, and after exercise. Electromyography (EMG) amplitude was recorded from the vastus lateralis during exercise.

RESULTS

Blood flow increased during exercise compared to rest across all cuff pressures (p < 0.001), however compared to 0%, the absolute blood flow was reduced by 34 ± 17%, 45 ± 22%, and 72 ± 19% for 60, 80, and 100% AOP, respectively. Furthermore, each cuff pressure resulted in similar relative changes in blood flow before, during, and after exercise. During exercise, tissue saturation index (TSI) decreased as cuff pressure increased (p ≤ 0.005) with the exception of 80 to 100% AOP. Deoxyhemoglobin increased (p ≤ 0.001) with cuff pressure.

CONCLUSION

Our data indicate that while BFR knee extension elicits an absolute hyperemic response at cuff pressures up to 100% resting AOP, the relative reductions in blood flow are consistent across rest, exercise and recovery.

Acute Neuromuscular and Microvascular Responses to Concentric and Eccentric Exercises With Blood Flow Restriction

Lauver, JD, Cayot, TE, Rotarius, TR, and Scheuermann, BW. Acute neuromuscular and microvascular responses to concentric and eccentric exercises with blood flow restriction. J Strength Cond Res 34(10): 2725-2733, 2020-The purpose of this study was to investigate the effects of the addition of blood flow restriction (BFR) during concentric and eccentric exercises on muscle excitation and microvascular oxygenation status. Subjects (N = 17) were randomly assigned to either a concentric (CON, CON + BFR) or eccentric (ECC, ECC + BFR) group, with one leg assigned to BFR and the other to non-BFR. Surface electromyography and near-infrared spectroscopy were used to measure muscle excitation and microvascular deoxygenation (deoxy-[Hb + Mb]) and [total hemoglobin concentration] during each condition, respectively. On separate days, subjects completed 4 sets (30, 15, 15, 15) of knee extension exercise at 30% maximal torque, and 1 minute of rest was provided between the sets. Greater excitation of the vastus medialis was observed during CON + BFR (54.4 ± 13.3% maximal voluntary isometric contraction [MVIC]) and ECC + BFR (53.0 ± 18.0% MVIC) compared with CON (42.0 ± 10.8% MVIC) and ECC (46.8 ± 9.6% MVIC). Change in deoxy-[Hb + Mb] was greater during CON + BFR (10.0 ± 10.4 μM) than during CON (4.1 ± 4.0 μM; p < 0.001). ECC + BFR (7.8 ± 6.7 μM) was significantly greater than ECC (3.5 ± 4.7 μM; p = 0.001). Total hemoglobin concentration was greater for ECC + BFR (7.9 ± 4.4 μM) compared with ECC (5.5 ± 3.5 μM). The addition of BFR to eccentric and concentric exercises resulted in a significant increase in metabolic stress and muscle excitation compared with non-BFR exercise. These findings suggest that although BFR may increase the hypertrophic stimulus during both modes of contraction, BFR during concentric contractions may result in a greater stimulus.

Effects of Running Exercise Combined With Blood Flow Restriction on Strength and Sprint Performance

Chen, YT, Hsieh, YY, Ho, JY, and Lin, JC. Effects of running exercise combined with blood flow restriction on strength and sprint performance. J Strength Cond Res XX(X): 000-000, 2019-We investigated muscle strength and sprint performance after combining running exercise (RE) with blood flow restriction (BFR). Twelve male sprinters received 2 experimental warm-ups: (a) RE (50% heart rate reserve, 2 minutes × 5 sets, 1-minute rest interval) with BFR (occlusion pressure: 1.3 × resting systolic blood pressure) warm-up, namely RE-BFR; and (b) RE without BFR warm-up, namely RE. Isokinetic strength or 60-m sprint performance was assessed after a 5-minute recovery from each experimental warm-up. All subjects completed 4 exercise trials in a counterbalanced order: (a) RE-BFR-strength; (b) RE-strength; (c) RE-BFR-sprint; and (d) RE-sprint. Muscle activation (during RE), blood lactate (BLa) (pre- and post-REs), heart rate (HR), and rating of perceived exertion (RPE) (pre- and post-REs and at a 5-minute recovery) were determined during each experimental warm-up. The isokinetic knee flexor strength and the hamstring-quadriceps (H:Q) ratio observed for the RE-BFR warm-up were significantly higher than those observed for the RE warm-up (p < 0.05). However, no differences (p > 0.05) in the isokinetic knee extensor strength and 60-m sprint performance were observed between the 2 warm-ups. Running exercise-BFR warm-up induced a higher level of vastus lateralis and biceps femoris muscle activation than did RE warm-up (p < 0.05). Furthermore, RE-BFR warm-up induced higher HR, RPE, and BLa values than did RE warm-up after RE and at a 5-minute recovery (p < 0.05). These results suggest that RE-BFR warm-up may augment physiological responses and improve the H:Q ratio and isokinetic knee flexor strength. Thus, RE-BFR warm-up may be considered a practical warm-up strategy for promoting muscle strength and reducing the risk of hamstring injury in male sprinters.

Blood flow restriction augments the skeletal muscle response during very low-load resistance exercise to volitional failure

The purpose of this study was to compare the acute muscular response with resistance exercise between the following conditions [labeled (% one-repetition maximum/% arterial occlusion pressure)]: high-load (70/0), very low-load (15/0), very low-load with moderate (15/40), and high (15/80) blood flow restriction pressures. Twenty-three participants completed four sets of unilateral knee extension to failure (up to 90 repetitions) with each condition, one condition per leg, each day. Muscle thickness and maximal voluntary contraction (MVC) were measured before (Pre), immediately after (Post-0), and 15 min after (Post-15) exercise and electromyography (EMG) amplitude during exercise. Pre to Post-0 muscle thickness changes in cm [95% CI] were greater with 15/40 [0.57 (0.41, 0.73)] and 15/80 [0.49 (0.35, 0.62)] compared to 70/0 [0.33 (0.25, 0.40)]. Pre to Post-0 MVC changes in Nm [95% CI] were higher with 15/40 [-127.0 (-162.1, -91.9)] and 15/80 [-133.6 (-162.8, -104.4)] compared to 70/0 [-48.4 (-70.1, -26.6)] and 15/0 [-98.4 (-121.9, -74.9)], which were also different. Over the first three repetitions, EMG increased across sets, whereas in the last three repetitions it did not. EMG was also different between conditions and was generally greater during 70/0. Repetitions decreased across sets reaching the lowest for 70/0, and for very low loads decreased with increased pressure. In trained participants exercising to failure, lower load and the application of restriction pressure augment changes in muscle thickness and torque. The EMG amplitude was augmented by load. Training studies should compare these conditions, as the results herein suggest some muscular adaptations may differ.

Blood-Flow Restricted Warm-Up Alters Muscle Hemodynamics and Oxygenation during Repeated Sprints in American Football Players

Team-sport athletes and coaches use varied strategies to enhance repeated-sprint ability (RSA). Aside from physical training, a well-conducted warm-up enhances RSA via increased oxidative metabolism. Strategies that impede blood flow could potentiate the effects of a warm-up due to their effects on the endothelial and metabolic functions. This study investigated whether performing a warm-up combined with blood-flow restriction (WFR) induces ergogenic changes in blood volume, muscle oxygenation, and RSA. In a pair-matched, single-blind, pre-post parallel group design, 15 American football players completed an RSA test (12 × 20 m, 20 s rest), preceded by WFR or a regular warm-up (SHAM). Pressure was applied on the athletes’ upper thighs for ≈15 min using elastic bands. Both legs were wrapped at a perceived pressure of 7 and 3 out of 10 in WFR and SHAM, respectively. Changes in gastrocnemius muscle oxygen saturation (S_mO₂) and total hemoglobin concentration ([THb]) were monitored with near-infrared spectroscopy. Cohen’s effect sizes (ES) were used to estimate the impact of WFR. WFR did not clearly alter best sprint time (ES −0.25), average speed (ES 0.25), total time (ES −0.12), and percent decrement score (ES 0.39). While WFR did not meaningfully alter average S_mO₂ and [THb], the intervention clearly increased the maximum [THb] and the minimum and maximum S_mO₂ during some of the 12 sprint/recovery periods (ES 0.34–1.43). Results indicate that WFR positively alters skeletal muscle hemodynamics during an RSA test. These physiological changes did not improve short-term RSA, but could be beneficial to players during longer activities such as games.

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.

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.

Impact of Blood Flow Restriction Exercise on Muscle Fatigue Development and Recovery

PURPOSE

The present study was designed to provide mechanistic insight into the time course and etiology of muscle fatigue development and recovery during and after low-intensity exercise when it is combined with blood flow restriction (BFR).

METHODS

Seventeen resistance-trained males completed four sets of low-intensity isotonic resistance exercise under two experimental conditions: knee extension exercise (i) with BFR and (ii) without BFR (CON). Neuromuscular tests were performed before, during (immediately after each set of knee extension exercise), and 1, 2, 4, and 8 min after each experimental condition. Maximal voluntary torque, quadriceps twitch torque in response to paired electrical stimuli at 10 Hz (PS10) and 100 Hz (PS100), PS10·PS100 ratio as an index of low-frequency fatigue, and voluntary activation were measured under isometric conditions. Perceptual and EMG data were recorded during each exercise condition.

RESULTS

After the first set of exercise, BFR induced significantly greater reductions in maximal voluntary torque, PS100, and PS10·PS100 ratio compared with CON. These parameters progressively declined throughout the BFR protocol but recovered substantially within 2 min postexercise when blood flow was restored. Neither a progressive decline in the course of the exercise protocol nor a substantial recovery of these parameters occurred during and after CON. Only at exercise termination, voluntary activation differed significantly between BFR and CON with greater reductions during BFR.

CONCLUSION

At the early stage of exercise, BFR exacerbated the development of muscle fatigue mainly due to a pronounced impairment in contractile function. Despite the high level of muscle fatigue during BFR exercise, the effect of BFR on muscle fatigue was diminished after 2 min of reperfusion, suggesting that BFR has a strong but short-lasting effect on neuromuscular function.