J. Grant Mouser

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.

Practicing the Test Produces Strength Equivalent To Higher Volume Training

Purpose To determine if muscle growth is important for increasing muscle strength or if changes in strength can be entirely explained from practicing the strength test. Methods Thirty-eight untrained individuals performed knee extension and chest press exercise for 8 wk. Individuals were randomly assigned to either a high-volume training group (HYPER) or a group just performing the one repetition maximum (1RM) strength test (TEST). The HYPER group performed four sets to volitional failure (~8RM–12RM), whereas the TEST group performed up to five attempts to lift as much weight as possible one time each visit. Results Data are presented as mean (90% confidence interval). The change in muscle size was greater in the HYPER group for both the upper and lower bodies at most but not all sites. The change in 1RM strength for both the upper body (difference of −1.1 [−4.8, 2.4] kg) and lower body (difference of 1.0 [−0.7, 2.8] kg for dominant leg) was not different between groups (similar for nondominant). Changes in isometric and isokinetic torque were not different between groups. The HYPER group observed a greater change in muscular endurance (difference of 2 [1,4] repetitions) only in the dominant leg. There were no differences in the change between groups in upper body endurance. There were between-group differences for exercise volume (mean [95% confidence interval]) of the dominant (difference of 11,049.3 [9254.6–12,844.0] kg) leg (similar for nondominant) and chest press with the HYPER group completing significantly more total volume (difference of 13259.9 [9632.0–16,887.8] kg). Conclusions These findings suggest that neither exercise volume nor the change in muscle size from training contributed to greater strength gains compared with just practicing the test.

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.

Correlations Do Not Show Cause and Effect: Not Even for Changes in Muscle Size and Strength

It is well known that resistance exercise results in increased muscle strength, but the cause of the improvement is not well understood. It is generally thought that initial increases in strength are caused by neurological factors, before being predominantly driven by increases in muscle size. Despite this hypothesis, there is currently no direct evidence that training-induced increases in muscle size contribute to training-induced increases in muscle strength. The evidence used to support this hypothesis is exclusively correlational analyses and these are often an afterthought using data collected to answer a different question of interest. Not only do these studies not infer causality, but they have inherent limitations associated with measurement error and limited inter-individual variability. To answer the question as to whether training-induced increases in muscle size lead to training-induced increases in strength requires a study designed to produce differential effects on muscle size based on group membership (i.e., one group increases muscle size and one does not) and observe how this impacts muscle strength. We have performed studies in our laboratory in which muscle strength increases similarly independent of whether muscle growth is or is not present, illustrating that the increases in muscle strength are not likely driven by increases in muscle size. The hypothesis that training-induced increases in muscle size contribute to training-induced increases in muscle strength requires more appropriately designed studies, and until such studies are completed, this statement should not be made as there are no data to support this hypothesis.

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 Cardiovascular and Perceptual Response to Very Low Load Blood Flow Restricted Exercise

This study sought to compare cardiovascular and perceptual responses to blood flow restriction (BFR) exercise using various pressure and load combinations. Fourteen participants completed four sets of BFR elbow flexion using 10, 15 and 20% 1RM with 40 and 80% arterial occlusion pressure (AOP). AOP was measured before and after exercise. Perceived exertion (RPE) and discomfort were assessed before exercise and after each set. Data presented as mean (95% CI), except for RPE and discomfort: 25th, 50th, 75th percentiles. AOP increased post-exercise (p<0.001) with larger magnitudes seen when increasing load and pressure (p<0.001) [e. g., 10/40 ΔAOP: 21 (10, 32) mmHg vs. 20/80 ΔAOP: 62 (45, 78) mmHg], which also augmented RPE (p<0.001) [e. g., 4th set 10/40: (7, 8.5, 12) vs. 4th set 20/80: (12.75, 15.5, 17.25)] and discomfort (p<0.001) [e. g., 4th set 10/40: (0.75, 2, 4.25) vs. 4th set 20/80: (4.25, 6, 8,)]. Volume increased via greater loads (p<0.001), and participants only reached failure during 20% 1RM conditions [20/40: 74 (74, 75) repetitions; 20/80: 71 (68, 75) repetitions]. When performing BFR exercise with very low loads the magnitudes of the cardiovascular and perceptual responses are augmented by increasing the load and by applying a higher relative pressure.

Are there perceptual differences to varying levels of blood flow restriction

The application of blood flow restriction (BFR) with low load exercise has been shown to produce favorable muscle and vascular adaptations. Given the potential clinical utility of BFR, it is important to characterize the ratings of perceived exertion (RPE) and discomfort across a variety of relative pressures as the individuals perceptual response may ultimately dictate whether a participant continues with this modality of exercise. Fourteen participants completed 3 days of exercise. Conditions included unilateral elbow flexion with six pressures ranging from 40% to 90% arterial occlusion at 30% of their one repetition maximum (1RM). Differences in RPE (6: no exertion at all, 20: maximal exertion) were found across conditions for set 2 (range of 13-15), 3 (range of 15-16), and 4 (range of 15-17). Following Bonferroni adjustments, none were significant. Differences in discomfort (0: no discomfort at all; 10: maximum discomfort) were found across conditions for set 1 (range of 2-3), 2 (range of 3.2-5), 3 (range of 4-6.5), and 4 (range of 5-7). Post-hoc analyses only found differences within set 3. Although it is presently unknown if higher pressures are required for optimal adaption of tissues other than skeletal muscle, our results suggest that the perceptual rating during exercise is unlikely to be a limiting factor in the application of higher pressures.