Scott J. Dankel

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

Participation in muscle-strengthening activities as an alternative method for the prevention of multimorbidity.

OBJECTIVE Participating in muscle-strengthening activities (MSA) has been shown to reduce the risks associated with many individual chronic diseases; however, the impact of MSA on multimorbidity remains unexplored. Therefore, the purpose of this study was to determine the association between MSA and multimorbidity. METHODS Data from the 2003-2006 NHANES were used including 4587 adults (≥20 years old). Participation in MSA was defined as self-reported involvement within the last 30 days. Multimorbidity was deemed as having ≥2 of the 14 chronic diseases. RESULTS After adjustments (including accelerometry-assessed physical activity), individuals participating in MSA had a 26% reduced odds of having multimorbidity (OR=0.74; 95% CI: 0.62-0.88; p=0.001) and each 2 day/week increase in MSA was associated with an 8% reduced odds of being multimorbid (OR=0.92; 95% CI: 0.84-1.00; p=0.05). CONCLUSION Independent of accelerometry-assessed physical activity, the participation in MSA may reduce the odds of being multimorbid, with evidence of a dose-response relationship.

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.

Combined Associations of Muscle-Strengthening Activities and Accelerometer-Assessed Physical Activity on Multimorbidity: Findings From NHANES.

Purpose. Physical activity (PA) has previously been demonstrated to be inversely related with multimorbidity (having more than one chronic disease); however, it is unknown whether dual participation in both PA and muscle-strengthening activities (MSA) may further reduce the odds of being multimorbid. Therefore, the purpose of our study was to determine the association between multimorbidity and individuals meeting recommended guidelines for both PA and MSA. Design. Nonexperimental. Setting. The 2003–2006 National Health and Nutritional Examination Survey. Subjects. Four thousand five hundred eighty-seven adults aged ≥20 years. Measures. Accelerometry-measured PA, self-reported MSA, and multimorbidity. Analysis. Data were analyzed using multivariable linear and logistic regression. Results. The odds (95% confidence interval) of being multimorbid for those only meeting MSA guidelines, only meeting PA guidelines, and meeting both PA and MSA guidelines (vs. not meeting either), respectively, were .69 (.48, .98; p = .04), .55 (.44, .70; p < .01), and .38 (.27, .53; p < .01). Conclusion. Our findings demonstrate that individuals meeting recommended guidelines for both MSA and PA were less likely to be multimorbid than individuals participating in one or none of these exercise modalities. Determining effective ways to initiate and maintain concurrent adoption of MSA and PA is needed to provide a cost-effective behavioral alternative for reducing the prevalence of multimorbidity.

Does the fat-but-fit paradigm hold true for all-cause mortality when considering the duration of overweight/obesity? Analyzing the WATCH (Weight, Activity and Time Contributes to Health) paradigm

BACKGROUND Physical activity has been shown to attenuate the association between overweight/obesity and mortality. Much less is known, however, on how the duration of overweight/obesity potentially alters this association, which was the purpose of this study. METHODS The 1999-2006 NHANES was used and 11,057 adults (ages 36-85) were evaluated. Eight mutually exclusive groups were created: (1) physically active, normal weight now and 10years ago; (2) physically inactive, normal weight now and 10years ago; (3) physically active, overweight/obese now but normal weight 10years ago; (4) physically inactive, normal weight now but overweight/obese 10years ago; (5) physically active, overweight/obese now but normal weight 10years ago; (6) physically inactive, overweight/obese now but normal weight 10years ago; (7) physically active, overweight/obese now and 10years ago; and (8) physically inactive, overweight/obese now and 10years ago. RESULTS After adjustments, only those individuals that were inactive were at a significantly increased risk for all-cause mortality independent of overweight/obesity status (Groups 2, 4, 6, 8). CONCLUSION In alignment with the Exercise is Medicine initiative®, our results provide support for clinicians to perform routine assessments of physical activity, and to further promote physical activity among all individuals regardless of body mass status.

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.

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.