Brittany R. Counts

Influence of relative blood flow restriction pressure on muscle activation and muscle adaptation.

Introduction: The aim of this study was to investigate the acute and chronic skeletal muscle response to differing levels of blood flow restriction (BFR) pressure. Methods: Fourteen participants completed elbow flexion exercise with pressures from 40% to 90% of arterial occlusion. Pre/post torque measurements and electromyographic (EMG) amplitude of each set were quantified for each condition. This was followed by a separate 8‐week training study of the effect of high (90% arterial occlusion) and low (40% arterial occlusion) pressure on muscle size and function. Results: For the acute study, decreases in torque were similar between pressures [–15.5 (5.9) Nm, P = 0.344]. For amplitude of the first 3 and last 3 reps there was a time effect. After training, increases in muscle size (10%), peak isotonic strength (18%), peak isokinetic torque (180°/s = 23%, 60°/s = 11%), and muscular endurance (62%) changed similarly between pressures. Conclusion: We suggest that higher relative pressures may not be necessary when exercising under BFR. Muscle Nerve 53: 438–445, 2016

The acute and chronic effects of “NO LOAD” resistance training

The purpose of the study was to remove the influence of an external load and determine if muscle growth can be elicited by maximally contracting through a full range of motion. In addition, the acute physiologic and perceptual responses to each stimulus were also investigated. Thirteen participants completed 18 sessions of unilateral elbow flexion exercise. Each arm was designated to either NO LOAD or HIGH LOAD condition (70% one repetition maximum). For the NO LOAD condition, participants repeatedly contracted as hard as they could through a full range of motion without the use of an external load. Our results show that anterior muscle thickness increased similarly from Pre to Post, with no differences between conditions for the 50% [Pre: 2.7 (0.8) vs. Post: 2.9 (0.7)], 60% [Pre: 2.9 (0.7) vs. Post: 3.1 (0.7)] or 70% [Pre: 3.2 (0.7) vs. Post: 3.5 (0.7)] sites. There was a significant condition×time interaction for one repetition maximum (p=0.017), with HIGH LOAD (+2.3kg) increasing more than the NO LOAD condition (+1kg). These results extend previous studies that have observed muscle growth across a range of external loads and muscle actions and suggest that muscle growth can occur independent of an external load provided there are enough muscle fibers undergoing mechanotransduction.

The problem Of muscle hypertrophy: Revisited

In this paper we revisit a topic originally discussed in 1955, namely the lack of direct evidence that muscle hypertrophy from exercise plays an important role in increasing strength. To this day, long‐term adaptations in strength are thought to be primarily contingent on changes in muscle size. Given this assumption, there has been considerable attention placed on programs designed to allow for maximization of both muscle size and strength. However, the conclusion that a change in muscle size affects a change in strength is surprisingly based on little evidence. We suggest that these changes may be completely separate phenomena based on: (1) the weak correlation between the change in muscle size and the change in muscle strength after training; (2) the loss of muscle mass with detraining, yet a maintenance of muscle strength; and (3) the similar muscle growth between low‐load and high‐load resistance training, yet divergent results in strength. Muscle Nerve 54: 1012–1014, 2016

Training to Fatigue: The Answer for Standardization When Assessing Muscle Hypertrophy?

Studies examining resistance training are of importance given that increasing or maintaining muscle mass aids in the prevention or attenuation of chronic disease. Within the literature, it is common practice to administer a set number of target repetitions to be completed by all individuals (i.e. 3 sets of 10) while setting the load relative to each individual’s predetermined strength level (usually a one-repetition maximum). This is done under the assumption that all individuals are receiving a similar stimulus upon completing the protocol, but this does not take into account individual variability with regard to how fatiguing the protocol actually is. Another limitation that exists within the current literature is the reporting of exercise volume in absolute or relative terms that are not truly replicable as they are both load-dependent and will differ based on the number of repetitions individuals can complete at a given relative load. Given that the level of fatigue caused by an exercise protocol is a good indicator of its hypertrophic potential, the most appropriate way to ensure all individuals are given a common stimulus is to prescribe exercise to volitional fatigue. While some authors commonly employ this practice, others still prescribe an arbitrary number of repetitions, which may lead to unfair comparisons between exercise protocols. The purpose of this opinion piece is to provide evidence for the need to standardize studies examining muscle hypertrophy. In our opinion, one way in which this can be accomplished is by prescribing all sets to volitional fatigue.

Muscle adaptations following 21 consecutive days of strength test familiarization compared with traditional training

Large increases in 1‐repetition maximum (1RM) strength have been demonstrated from repeated testing, but it is unknown whether these increases can be augmented by resistance training.

Blood flow occlusion pressure at rest and immediately after a bout of low load exercise.

The purpose of this study was to determine whether arm circumference is predictive of arterial occlusion in the standing position and to determine the change in pressure before and immediately after exercise. Thirty‐one participants had their arm circumference, blood pressure and standing arterial occlusion determined before exercise. Participants then completed elbow flexions at 40% of resting arterial occlusion at 30% of their one repetition maximum (1RM). The goal repetitions for the exercise included one set of 30 repetitions followed by 3 sets of 15, with 30s rest between sets. Immediately following the last set, postexercise arterial occlusion was determined. Two different models of hierarchical linear regression were used to determine the greatest predictor of standing arterial occlusion. Our final model explained 69% of the variance in arterial occlusion with arm circumference (β = 0·639, part = 0·568) explaining more than brachial systolic blood pressure (β = 0·312, part = 0·277). Standing arterial occlusion increased from pre‐ [138 (15) mmHg] to post‐ [169 (20) mmHg] exercise (P<0·001). In conclusion, the cardiovascular response to blood flow restriction (BFR) in the upper arm following 4 sets of elbow flexion exercise decreases the relative arterial occlusion pressure. In addition, we confirm previous data that circumference explains the most unique variance in arterial occlusion pressure in the upper body. These findings are important as they provide additional insight into making the pressure more uniform between participants throughout exercise.

The widespread misuse of effect sizes

OBJECTIVES Studies comparing multiple groups (i.e., experimental and control) often examine the efficacy of an intervention by calculating within group effect sizes using Cohens d. This method is inappropriate and largely impacted by the pre-test variability as opposed to the variability in the intervention itself. Furthermore, the percentage change is often analyzed, but this is highly impacted by the baseline values and can be potentially misleading. Thus, the objective of this study was to illustrate the common misuse of the effect size and percent change measures. DESIGN Here we provide a realistic sample data set comparing two resistance training groups with the same pre-test to post-test change. METHODS Statistical tests that are commonly performed within the literature were computed. RESULTS Analyzing the within group effect size favors the control group, while the percent change favors the experimental group. The most appropriate way to present the data would be to plot the individual responses or, for larger samples, provide the mean change and 95% confidence intervals of the mean change. This details the magnitude and variability within the response to the intervention itself in units that are easily interpretable. CONCLUSIONS This manuscript demonstrates the common misuse of the effect size and details the importance for investigators to always report raw values, even when alternative statistics are performed.

Muscle growth: To infinity and beyond?

Strength increases following training are thought to be influenced first by neural adaptions and second by large contributions from muscle growth. This is based largely on the idea that muscle growth is a slow process and that a plateau in muscle growth would substantially hinder long‐term increases in strength. This Review examines the literature to determine the time course of skeletal muscle growth in the upper and lower body and to determine whether and when muscle growth plateaus. Studies were included if they had at least 3 muscle size time points, involved participants 18 years or older, and used a resistance training protocol. Muscle growth occurs sooner than had once been hypothesized, and this adaptation is specific to the muscle group. Furthermore, the available studies indicate that the muscle growth response will plateau, and additional growth is not likely to occur appreciably beyond this initial plateau. However, the current study durations are a limitation. Muscle Nerve 56: 1022–1030, 2017

The effects of upper body exercise across different levels of blood flow restriction on arterial occlusion pressure and perceptual responses.

Recent studies have investigated relative pressures that are applied during blood flow restriction exercise ranging from 40%-90% of resting arterial occlusion pressure; however, no studies have investigated relative pressures below 40% arterial occlusion pressure. The purpose of this study was to characterize the cardiovascular and perceptual responses to different levels of pressures. Twenty-six resistance trained participants performed four sets of unilateral elbow flexion exercise using 30% of their 1RM in combination with blood flow restriction inflated to one of six relative applied pressures (0%, 10%, 20%, 30%, 50%, 90% arterial occlusion pressure). Arterial occlusion pressure was measured before (pre) and immediately after the last set of exercise at the radial artery. RPE and discomfort were taken prior to (pre) and following each set of exercise. Data presented as mean (95% CI) except for perceptual responses represented as the median (25th, 75th percentile). Arterial occlusion pressure increased from pre to post (p<0.001) in all conditions but was augmented further with higher pressures [e.g. 0%: 36 (30-42) mmHg vs. 10%: 39 (34-44) mmHg vs. 90% 46 (41-52) mmHg]. For RPE and discomfort, there were significant differences across conditions for all sets of exercise (p<0.01) with the ratings of RPE [e.g. 0%: 14.5 (13, 17) vs. 10%: 13.5 (12, 17) vs. 90%: 17 (14.75, 19) during last set] and discomfort [e.g. 0%: 3.5 (1.5, 6.25) vs. 10%: 3 (1, 6) vs. 90%: 7 (4.5, 9) during last set] generally being greater at the higher restriction pressures. All of these differences at the higher restriction pressures occurred despite completing a lower total volume of exercise. Applying higher relative pressures results in the greatest cardiovascular response, higher perceptual ratings, and greater decrease in exercise volume compared to lower restriction pressures. Therefore, the perceptual responses from lower relative pressures may be more appealing and provide a safer and more tolerable stimulus for individuals.

Blood Flow in Humans Following Low-Load Exercise with and without Blood Flow Restriction

Blood flow restriction (BFR) in combination with exercise has been used to increase muscle size and strength using relatively low loads (20%-30% 1-repetition maximum (1RM)). In research, the range of applied pressures based on a percentage of arterial occlusion pressure (AOP), is wide. The purpose of the study is to measure the blood flow response before exercise, following each set of exercise, and postexercise to low-load elbow flexion combined with no restriction (NOBFR), 40% of AOP (40BFR), and 80% of AOP (80BFR). One hundred and fifty-two participants volunteered; 140 completed the protocol (women = 75, men = 65). Participants were counter-balanced into 1 of 3 conditions. Following AOP and 1RM measurement, ultrasound was used to measure standing blood flow at rest in the right brachial artery. Participants performed 4 sets of elbow flexion at 30% 1RM. Blood flow was measured between sets and at 1 and 5 min postexercise. Blood flow decreased following inflation, with no difference between conditions (p < 0.001). Men had greater blood flow than women in all conditions at all time points (p < 0.001). Resting hyperemia decreased with pressure (NOBFR > 40BFR > 80BFR, p < 0.001). Blood flow increased from rest to after set 1 regardless of condition. Following cuff deflation, blood flow increased in both the 80BFR and 40BFR conditions. The reduction in hyperemia during BFR is pressure-dependent. Contrary to previous investigations, blood flow was increased above baseline following exercise.