Isometric blood flow restriction exercise: acute physiological and neuromuscular responses

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.

Can We Make Blood Flow Restriction Training More Accessible? Validity of a Low-Cost Blood Flow Restriction Device to Estimate Arterial Occlusion Pressure

ABSTRACT

Keller, M, Faude, O, Gollhofer, A, and Centner, C. Can we make blood flow restriction training more accessible? Validity of a low-cost blood flow restriction device to estimate arterial occlusion pressure. J Strength Cond Res 37(8): 1581-1587, 2023-Evidence indicates that low-load resistance training with blood flow restriction (BFR) results in comparable gains in muscle mass and muscle strength as high-load resistance training without BFR. Low-load BFR training is a promising tool for areas such as rehabilitation because individuals are exposed to low mechanical stress. However, BFR training is only safe and effective when the cuff pressure is individually adjusted to the arterial occlusion pressure (AOP). Generally, thresholds for AOP are typically determined with sophisticated laboratory material, including Doppler ultrasound and tourniquet systems. Therefore, this study investigated the validity of a low-cost BFR product with automatic AOP assessment (AirBands International) compared with the gold standard for determining the individual AOP. Valid measurements were obtained at the arms and legs in 104 healthy volunteers. For the arms ( n = 49), a Bland-Altman analysis revealed a mean difference of 7 ± 13 mm Hg between the 2 methods, with slightly higher pressure levels for the gold standard (131 ± 14 mm Hg) than for the low-cost device (125 ± 17 mm Hg). For the legs ( n = 55), the low-cost device reached its maximum pressure capacity in 70% of subjects during AOP identification, making the results on the legs unreliable. Although the low-cost device is a valid tool for identifying the individual AOP in the arms, the device cannot be recommended for use at the legs because of its limited pressure capacity. When using the low-cost device for BFR training at the arms, it is recommended to apply the cuff pressure to 60% of the individual AOP to meet current BFR training guidelines.

Exercised-Induced Hypoalgesia following An Elbow Flexion Low-Load Resistance Exercise with Blood Flow Restriction: A Sham-Controlled Randomized Trial in Healthy Adults

We aimed to evaluate the hypoalgesic effect of an elbow flexion low-load resistance exercise with blood flow restriction (LLRE-BFR) when compared to high-load resistance exercise (HLRE) with sham-BFR in healthy individuals. Forty healthy young adults (17 women), with a mean age ± SD: 26.6 ± 6.8 years, and mean body mass index ± SD: 23.6 ± 2.7 were randomly assigned to either an LLRE-BFR (30% 1 repetition maximum, RM) or an HLRE with sham-BFR group (70% of 1 RM). Blood pressure and pressure pain thresholds (PPTs) were measured pre- and post-exercise intervention. The rating of perceived exertion (RPE) was recorded after each set. There were non-significant between-group changes in PPT at the dominant biceps (-0.61, 95%CI: -1.92 to 0.68) with statistically significant reductions between pre- and post-exercise in LLRE-BFR (effect size, d = 0.88) and HLRE-BFR (effect size, d = 0.52). No within- or between-group differences were recorded in PPT at non-exercising sites of measurement. No mediating effects of changes in blood pressure or RPE on the changes in pressure pain threshold were observed. LLRE-BFR produced a similar hypoalgesic effect locally compared to HLRE and can be used as an alternative intervention to decrease pain sensitivity when HLRE is contraindicated or should be avoided.

Sustained acoustic medicine for the treatment of musculoskeletal injuries: a systematic review and meta-analysis

BACKGROUND

Musculoskeletal injuries account for 10 million work-limited days per year and often lead to both acute and/or chronic pain, and increased chances of re-injury or permanent disability. Conservative treatment options include various modalities, nonsteroidal anti-inflammatory drugs, and physical rehabilitation programs. Sustained Acoustic Medicine is an emerging prescription home-use mechanotransductive device to stimulate cellular proliferation, increase microstreaming and cavitation in situ, and to increase tissue profusion and permeability. This research aims to summarize the clinical evidence on Sustained Acoustic Medicine and measurable outcomes in the literature.

METHODS

A systematic literature review was conducted using PubMed, EBSCOhost, Academic Search Complete, Google Scholar and ClinicalTrials.gov to identify studies evaluating the effects of Sustained Acoustic Medicine on the musculoskeletal system of humans. Articles identified were selected based on inclusion criteria and scored on the Downs and Black checklist. Study design, clinical outcomes and primary findings were extracted from included studies for synthesis and meta-analysis statistics.

RESULTS

A total of three hundred and seventy-two participants (372) were included in the thirteen clinical research studies reviewed including five (5) level I, four (4) level II and four (4) level IV studies. Sixty-seven (67) participants with neck and back myofascial pain and injury, one hundred and fifty-six (156) participants with moderate to severe knee pain and radiographically confirmed knee osteoarthritis (Kellgren-Lawrence grade II/III), and one hundred forty-nine (149) participants with generalized soft-tissue injury of the elbow, shoulder, back and ankle with limited function. Primary outcomes included daily change in pain intensity, change in Western Ontario McMaster Osteoarthritis Questionnaire, change in Global Rate of Change, and functional outcome measures including dynamometry, grip strength, range-of-motion, and diathermic heating (temperature measurement).

CONCLUSION

Sustained Acoustic Medicine treatment provides tissue heating and tissue recovery, improved patient function and reduction of pain. When patients failed to respond to physical therapy, Sustained Acoustic Medicine proved to be a useful adjunct to facilitate healing and return to work. As a non-invasive and non-narcotic treatment option with an excellent safety profile, Sustained Acoustic Medicine may be considered a good therapeutic option for practitioners.

Low-Load Blood Flow Restriction and High-Load Resistance Training Induce Comparable Changes in Patellar Tendon Properties

INTRODUCTION

Low-load resistance training with blood flow restriction (LL-BFR) has emerged as a viable alternative to conventional high-load (HL) resistance training regimens. Despite increasing evidence confirming comparable muscle adaptations between LL-BFR and HL resistance exercise, only very little is known about tendinous mechanical and morphological adaptations following LL-BFR. Therefore, the aim of the present study was to examine the effects of 14 weeks of LL-BFR and HL training on patellar tendon adaptations.

METHODS

N = 29 recreationally active male participants were randomly allocated into the following two groups: LL-BFR resistance training (20-35% one repetition maximum/1RM) or HL resistance training (70-85% 1RM). Both groups trained three times per week for 14 weeks. One week before and after the intervention, patellar tendon mechanical and morphological properties were assessed via ultrasound and magnetic resonance imaging (MRI). Additionally, changes in muscle cross-sectional area (CSA) were quantified by MRI and muscle strength via dynamic 1RM measurements.

RESULTS

The findings demonstrated that both LL-BFR and HL training resulted in comparable changes in patellar tendon stiffness (LL-BFR: + 25.2%, p = 0.003; HL: + 22.5%, p = 0.024) without significant differences between groups. Similar increases in tendon CSA were observed in HL and LL-BFR. Muscle mass and strength also significantly increased in both groups but were not statistically different between HL (+ 38%) and LL-BFR (+ 34%), except for knee extension 1RM where higher changes were seen in LL-BFR.

CONCLUSION

The present results support the notion that both HL and LL-BFR cause substantial changes in patellar tendon properties and the magnitude of changes are not significantly different between conditions. Further studies are needed which examine the physiological mechanisms underlying the altered tendon properties following LL-BFR training.

Effects of isometric handgrip exercise with or without blood flow restriction on interference control and feelings

The purpose of this study was to investigate whether isometric handgrip exercise, with or without blood flow restriction, would alter interference control and feelings. 60 healthy young adults completed three experimental visits, consisting of four sets of 2 min isometric handgrip exercise, at 30% of maximal strength with or without blood flow restriction (50% of arterial occlusion pressure), or a non-exercise/time-matched control. Exercise-induced feeling inventory and Stroop Color Word Test were performed at pre- and ~10-min post-exercise, respectively. Bayes factors (BF₁₀ ) quantified the evidence for or against the null. There were no changes or differences between conditions for interference control following exercise with or without blood flow restriction (Incongruent BF₁₀ : 0.155; Stroop Interference BF₁₀ : 0.082). There were also no differences in the error rate as well as no differences between conditions for changes in 'positivity' or 'revitalization'. Feelings of 'tranquility' were reduced relative to a control following exercise with (median δ [95% credible interval]: -0.74 (-1.05, -0.45), BF₁₀ : 5515.7) and without (median δ: -0.72 [-1.02, -0.41], BF₁₀ : 571.3) blood flow restriction. These changes were not different between exercise conditions. Feelings of 'physical exhaustion' were increased relative to a control following exercise without blood flow restriction (median δ: 0.35[0.09, 0.61], BF₁₀ : 5.84). However, this increase was not different from the same exercise with blood flow restriction. These results suggest that 1) isometric handgrip exercise could be performed without impairing interference control, even when blood flow restriction is added, and that 2) changes in feelings occur independent of changes in interference control.

Effect of 10 consecutive days of remote ischemic preconditioning on local neuromuscular performance

BACKGROUND

Most studies focus on the effects of a single remote ischemic preconditioning (RIPC) session on performance. However, the training-like effect of repeat RIPC sessions performed on consecutive days could potentially be even more beneficial to neuromuscular performance than a single RIPC session. Therefore, aim of the study was to assess the impact of 10 days of RIPC on local neuromuscular performance.

METHODS

Thirty-seven male participants performed 10 days of either RIPC or sham-controlled condition. Before and after procedure, the maximal voluntary contraction and muscle fatigue were assessed by dynamometry and surface electromyography (EMG) of the isometric extension of the knee joint. The following neuromuscular outcomes were investigated: peak torque (PKTQ); rate of force development (RTD); time to failure; and the slope of median frequency of power spectrum (MDF) and EMG amplitude.

RESULTS

After RIPC, while there was no change in PKTQ and time to failure, the late RTD and MDF slope were significantly affected. The RTD at 0-100 and 0-200 ms showed 24 and 16% increase, respectively, while the MDF slope showed 24% decrease in rectus femoris.

CONCLUSIONS

10 days of RIPC induced neuromuscular performance changes in the quadriceps muscle. Even though there were no changes in task to failure performance, RIPC showed EMG changes limited to rectus femoris and increased late RTD in MVC task.