Low-intensity blood-flow restriction (BFR) resistance training significantly increases strength and muscle size, but some studies report it produces exercise-induced muscle damage (EIMD) in the lower body after exercise to failure.
To investigate the effects of a pre-set number of repetitions of upper body concentric and eccentric exercise when combined with BFR on changes in EIMD.
Ten young men had arms randomly assigned to either concentric BFR (CON-BFR) or eccentric BFR (ECC-BFR) dumbbell curl exercise (30% one-repetition maximum (1-RM), 1 set of 30 repetitions followed by 3 sets of 15 repetitions). Maximal isometric voluntary contraction force (MVC), muscle thickness (MTH), circumference, range of motion (ROM), ratings of perceived exertion (RPE), and muscle soreness were measured before, immediately after, and daily for 4 days post-exercise.
MVC decreased by 36% for CON-BFR and 12% for ECCBFR immediately after exercise but was not changed 1–4 days post-exercise (p > 0.05). Only CON-BFR had significant changes in MTH and circumference immediately after exercise (p < 0.05). Muscle soreness was observed in the ECC-BFR arm at 1 and 2 days after exercise.
Low-intensity ECC-BFR produces significant muscle soreness at 24 h but neither ECC-BFR nor CON-BFR exercise produces significant changes in multiple indices of EIMD.
It was unknown whether ultrasound-measured forearm muscle thickness was impacted by pronation of the forearm. The aim of this study was to investigate the influence of forearm pronation on two forearm muscle thicknesses (MT-ulna and MT-radius).
Participants and Methods
Fourteen healthy children and adolescents sat on a chair with their right arm comfortably on a table, and their hands were fixed to the board with elastic bands. The probe was placed perpendicularly over the forearm, and the angle of the board was then pronated in 5° increments from −10° to 30°. The average value of the two measures at each angle was used.
There was evidence that MT-ulna differed across measurement sites (F = 51.086, P < 0.001). For example, the values of the MT-ulna were 2.58 (SD 0.40) cm in standard position (0°), 2.56 (SD 0.41) in −10°, 2.62 (SD 0.41) in 10°, 2.65 (SD 0.42) in 20°, and 2.71 (SD 0.43) in 30°. Follow-up tests found that all sites differed from each other except for −10° and −5° (P = 0.155) and 10° and 15° (P = 0.075). There was also evidence that the MT-radius differed across measurement sites (F = 22.07, P < 0.001). Follow-up tests found that many but not all sites differed from each other.
Our results suggest that MT-ulna increases and MT-radius decreases due to forearm pronation from the standard position (0°). When determining the forearm position using the 95% limits of agreement, we recommend the forearm position within ±5° of the standard forearm position when measuring forearm MT.
To remain independent and healthy, an important factor to consider is the maintenance of skeletal muscle mass. Inactivity leads to measurable changes in muscle and bone, reduces exercise capacity, impairs the immune system, and decreases the sensitivity to insulin. Therefore, maintaining physical activity is of great importance for skeletal muscle health. One form of structured physical activity is resistance training. Generally speaking, one needs to lift weights at approximately 70% of their one repetition maximum (1RM) to have noticeable increases in muscle size and strength. Although numerous positive effects are observed from heavy resistance training, some at risk populations (e.g. elderly, rehabilitating patients, etc.) might be advised not to perform high-load resistance training and may be limited to performance of low-load resistance exercise. A technique which applies pressure cuffs to the limbs causing blood flow restriction (BFR) has been shown to attenuate atrophy and when combined with low intensity exercise has resulted in an increase in both muscle size and strength across different age groups. We have provided an evidence based model of progression from bed rest to higher load resistance training, based largely on BFR literature concentrating on more at risk populations, to highlight a possible path to recovery.
The purpose of this study was to investigate the potential mechanisms behind the blood flow restriction (BFR) stimulus in the absence of exercise. Nine participants completed a 10 minute time control and then a BFR protocol. The protocol was five, 5-minute bouts of inflation with 3-minutes of deflation between each bout. The pressure was set relative to each individual’s thigh circumference. Significant increases in muscle thickness were observed for both the vastus lateralis (VL) [6%, p = 0.027] and rectus femoris (RF) [22%, p = 0.001] along with a significant decrease in plasma volume [15%, p = 0.001]. Ratings of discomfort during the BFR protocol peaked at 2.7 (light discomfort). There were no significant changes with whole blood lactate, electromyography (EMG), or heart rate (HR), however, there was a trend for a significant increase in HR during the 5th inflation (p = 0.057). In conclusion, this is the first study to demonstrate that the attenuation of both muscle atrophy and declines in strength previously observed with brief applications of BFR may have been mediated through an acute fluid shift induced increase in muscle size. This is supported by our finding that the changes in muscle thickness are maintained even after the cuffs have been removed.
The purpose of this study was to investigate the time course of hypertrophic adaptations in both the upper arm and trunk muscles following high-intensity bench press training. Seven previously untrained young men (aged 25±3 years) performed free-weight bench press training 3 days (Monday, Wednesday and Friday) per week for 24 weeks. Training intensity and volume were set at 75% of one repetition maximum (1-RM) and 30 repetitions (3 sets of 10 repetitions, with 2–3 min of rest between sets), respectively. Muscle thickness (MTH) was measured using B-mode ultrasound at three sites: the biceps and triceps brachii and the pectoralis major. Measurements were taken a week prior to the start of training, before the training session on every Monday and 3 days after the final training session. Pairwise comparisons from baseline revealed that pectoralis major MTH significantly increased after week-1 (p=0.002), triceps MTH increased after week-5 (p=0.001) and 1-RM strength increased after week-3 (p=0.001) while no changes were observed in the biceps MTH from baseline. Significant muscle hypertrophy was observed earlier in the chest compared to that of the triceps. Our results indicate that the time course of the muscle hypertrophic response differs between the upper arm and chest.
Grip strength is a marker of future health conditions and is mainly generated by the extrinsic flexor muscles of the fingers. Therefore, whether or not there is a relationship between grip strength and forearm muscle size is vital in considering strategies for grip strength development during growth. Thus, this study aimed to examine the association between changes in grip strength and forearm muscle thickness in young children.
Two hundred eighteen young children (104 boys and 114 girls) performed maximum voluntary grip strength and ultrasound-measured muscle thickness measurements in the right hand. Two muscle thicknesses were measured as the perpendicular distance between the adipose tissue-muscle interface and muscle-bone interface of the radius (MT-radius) and ulna (MT-ulna). All participants completed the first measurement and underwent a second measurement one year after the first one.
There were significant (P < 0.001) within-subject correlations between MT-ulna and grip strength [r = 0.50 (0.40, 0.60)] and MT-radius and grip strength [r = 0.59 (0.49, 0.67)]. There was no significant between-subject correlation between MT-ulna and grip strength [r = 0.07 (−0.05, 0.20)], but there was a statistically significant (P < 0.001) between-subject relationship between MT-radius and grip strength [r = 0.27 (0.14, 0.39)].
Although we cannot infer causation from the present study, our findings suggest that as muscle size increases within a child, so does muscle strength. Our between-subject analysis, however, suggests that those who observed the greatest change in muscle size did not necessarily get the strongest.
Blood flow restriction (BFR) combined with low load resistance training has been shown to result in muscle hypertrophy similar to that observed with higher loads. However, not all studies have found BFR efficacious, possibly due to methodological differences. It is presently unclear whether there are differences between cuffs of similar size (5 cm) but different material (nylon vs. elastic). The purpose was to determine if there are differences in repetitions to fatigue and perceptual ratings of exertion (RPE) and discomfort between narrow elastic and narrow nylon cuffs. Sixteen males and females completed three sets of BFR knee extension exercise in a randomized cross-over design using either elastic or nylon restrictive cuffs applied at the proximal thigh. There were no differences in repetitions to fatigue (marker of blood flow) or perceptual ratings between narrow elastic and narrow nylon cuffs. This data suggests that either elastic or nylon cuffs of the same width should cause similar degrees of BFR at the same pressure during resistance exercise.
It has been observed that gluteal-femoral adipose tissue has a protective effect against risk factors for cardiovascular disease but has not yet been concluded how different evaluation methods of fat distribution affect the results.
To test the hypothesis that B-mode ultrasound-measured subcutaneous adipose tissue distribution is associated with cardiovascular risk factors, 326 Japanese unmedicated postmenopausal women aged 50–70 years were analyzed. Subcutaneous adipose tissue thickness at 6 sites (anterior and posterior aspects of trunk, upper-arm, and thigh) and serum total (TC) and high-density lipoprotein cholesterol (HDLC) was measured, and a ratio of HDLC to TC (HDLC/TC) was calculated. We used Bayesian linear regression with 4 separate models with each model predicting HDLC/TC.
Our first model provided evidence for an inverse correlation (r = –0.23) between ultrasound measured body fat (6 site measurement) and HDLC/TC. The second model noted evidence for an inverse correlation between trunk fat and HDLC/TC and found evidence for the null with respect to the correlation between thigh fat and HDLC/TC. Therefore, we added thigh fat to the null model to produce Distribution Model 2. Within this model, we noted an inverse correlation (r = –0.353) between trunk fat and HDLC/TC. Our last model determined that within the trunk fatness, the abdominal area (anterior trunk) was a larger predictor than the subscapular site (posterior trunk).
These results support the evidence that ultrasound-measured abdominal subcutaneous adipose tissue thickness is a non-invasive predictor for monitoring the risk for dyslipidemia in postmenopausal women.
Orthostatic intolerance occurs in some astronauts following space flight. Although orthostatic blood pressure responses should normalize in the weeks following the return to Earth, there may be situations where an immediate short-term solution is necessary (e.g., emergency evacuation).
The purpose of this study was to examine different levels of blood flow restriction on changes in blood pressure and heart rate when transitioning from supine to a head-up tilt and determine whether this change differs based on sex.
Eighty-nine participants (45 men, 44 women) completed the three visits with different pressures (Sham, Moderate, and High) in a randomized order. Cuffs were placed on the most proximal area of the thighs. Brachial blood pressure was measured at baseline, upon inflation of the cuffs in a supine position, immediately after tilt (70°), and eight more times separated by 45 seconds.
Data are presented as mean (SD). The change in systolic (High > Moderate > Sham) [High vs Sham: 5.5 (7.4) mmHg, High vs Moderate: 3 (7.4) mmHg, and Moderate vs Sham: 2.4 (8.4) mmHg] and diastolic pressure (High > Moderate = Sham) [High vs Sham: 2.4 (5.3) mmHg, High vs Moderate: 1.9 (6.3) mmHg] differed across applied pressures. The change in heart rate was initially greatest in the sham-pressure but increased the greatest in the high-pressure condition by the end of the head-up tilt period. Additionally, there was no influence of sex.
Blood flow restriction applied in this study increased blood pressure in a pressure-dependent manner upon head-up tilt.
Previous work has found that wide cuffs produce greater discomfort with elbow flexion exercise than narrower cuffs. It is our hypothesis that this is due to the balling up of the biceps underneath the cuff that is more pronounced with a wider cuff. One method to test this is through an upper body exercise where there is no contraction of the biceps.
To investigate the effects of cuff width on discomfort following isometric handgrip exercise.
One hundred participants completed this experiment. In a randomized order, the participants performed four sets of two-minute isometric handgrip contractions with thirty seconds of rest at thirty percent of their maximal voluntary contraction with a 5 and 12 cm cuff inflated to 40% of arterial occlusion pressure. Discomfort ratings (0–100) were given after the fourth set of exercise. Average force was recorded for all four sets.
There was no difference in discomfort (BF10 = 0.158) [median difference (95% credible interval) −0.997 (−3.360, 1.283) arbitrary units], or in average force (BF10 = 0.132) [median difference (95% credible interval) 0.08 (−0.199, 0.372) kilograms], between cuff conditions. There did not appear to be a greater preference for either cuff. Forty people preferred the narrow cuff (BF10 = 0.325), forty people preferred the wide cuff (BF10 = 0.325), and twenty people had no preference (BF10 = 7.719).
Cuff width does not appear to influence discomfort or the average force produced. This provides support for our hypothesis that the shape of the muscle may interact with wider cuff sizes, leading to greater discomfort.