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- Author or Editor: J. Loenneke x
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Low-intensity resistance exercise with blood flow restriction (BFR) has been shown to induce a prominent increase in muscle activation in response to muscle fatigue. However, the magnitude of muscle fatigue between continuous (Con-BFR) and intermittent BFR (Int-BFR, BFR only during exercise) is currently unknown. We examined the effect of Con-BFR or Int-BFR on muscle activation during exercise. Unilateral arm curl exercise (20% of one-repetition maximum, four sets, 30 sec rest period between sets) was performed without (CON) or with Con-BFR or Int-BFR. During BFR conditions, the cuff was inflated to 160 mmHg on the proximal region of testing arm. Surface electromyography (EMG) was recorded from the biceps brachii muscle, and integrated EMG (iEMG) was analyzed. During the exercise, iEMG increased progressively in Con-BFR and Int-BFR and both conditions were greater (p < 0.05) than CON at the 3rd and 4th set. However, there were no differences (p > 0.05) in iEMG between Con-BFR and Int-BFR during exercise (∼2.45 and ∼2.40 times, respectively). Thus, the magnitude of increase in muscle activation may be similar between Con-BFR and Int-BFR when BFR exercise was performed at a high level of cuff pressure intensity.
Cycle training is widely performed as a major part of any exercise program seeking to improve aerobic capacity and cardiovascular health. However, the effect of cycle training on muscle size and strength gain still requires further insight, even though it is known that professional cyclists display larger muscle size compared to controls. Therefore, the purpose of this review is to discuss the effects of cycle training on muscle size and strength of the lower extremity and the possible mechanisms for increasing muscle size with cycle training. It is plausible that cycle training requires a longer period to significantly increase muscle size compared to typical resistance training due to a much slower hypertrophy rate. Cycle training induces muscle hypertrophy similarly between young and older age groups, while strength gain seems to favor older adults, which suggests that the probability for improving in muscle quality appears to be higher in older adults compared to young adults. For young adults, higher-intensity intermittent cycling may be required to achieve strength gains. It also appears that muscle hypertrophy induced by cycle training results from the positive changes in muscle protein net balance.
To investigate the relationships between site-specific muscle loss in the thigh, muscle quality and zigzag walking performance, 40 men and 41 women aged 65–79 years had muscle thickness (MTH) measured by ultrasound at nine sites on the anterior and posterior aspects of the body. Skeletal muscle mass (SM) was estimated from an ultrasoundderived prediction equation. Site-specific thigh sarcopenia was calculated using ultrasound-measured MTH at the anterior/posterior aspects of the thigh (AP-MTH ratio). Zigzag walking time (ZWT) and maximum isometric knee extension (KE) and flexion (KF) torques were measured. Muscle quality (torque/thigh SM) and knee joint strength index (torque/body mass) were calculated. There were no significant correlations between SM index and ZWT. However, AP-MTH ratio was inversely correlated (P < 0.05) to ZWT in men (r = −0.335) and women (r = −0.309). ZWT was also inversely correlated (P < 0.05) to KE-strength index in both sexes (men, r = −0.328; women, r = −0.372). Similarly, ZWT was correlated to KF-strength index (r = −0.497) and muscle quality (r = −0.322) in women, but not in men. After adjusting for age, height and body mass, AP-MTH ratio was inversely correlated to ZWT in men (r = −0.325) and tended to be correlated to ZWT in women (r = −0.263). Zigzag walking performance may be associated with site-specific thigh sarcopenia in older men and women.
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.
Previous studies reported that aerobic-type exercise such as walking or cycling with blood flow restriction (BFR) has been shown to elicit increases in leg muscle hypertrophy and strength, as well as improved aerobic capacity. Although previous studies investigated cardiovascular responses during a relatively short duration of exercise (∼5 min), the effects of prolonged leg muscular BFR have remained unknown. The purpose of this study was to examine the cardiovascular effects of longer duration low intensity exercise combined with BFR. Eight men performed 30 min of exercise at 40% of a predetermined maximal oxygen uptake under both BFR and normal flow (CON) conditions. Cardiovascular parameters were measured at rest and every 10 min during exercise. The main findings were that 1) the SV and HR did not change significantly between 10 to 30 min of exercise in BFR and CON conditions, although BFR-induced reduction of SV and increased HR were found at 10 min exercise compared with normal flow, 2) blood pressure was increased at 10 min of exercise in BFR compared to the CON, however the blood pressure decreased gradually with BFR from 10 to 30 min of exercise, and 3) blood lactate and RPE increased gradually during exercise with BFR. In conclusion, our results suggest that the BFR-induced reduction of SV and increased HR within the first 10 min of exercise are representative of changes in these parameters.
In order to ascertain whether differing structural mechanisms could underlie blood flow restricted training (BFRT) and high intensity training (HIT), this study had two aims: (i) to gain an insight into the acute variations of muscle architecture following a single bout of two different volumes of BFRT, and (ii) to compare these variations with those observed after HIT. Thirty-five young men volunteered for the study and were randomly divided into three groups: BFRT low volume (BFRT LV), BFRT high volume (BFRT HV) and traditional high intensity resistance training (HIT). All subjects performed a bilateral leg extension exercise session with a load of 20% of one repetition maximum (1RM) in the BFRT groups, whereas the load of the HIT group was equivalent to an 85% of their 1RM. Before and immediately after the exercise bout, ultrasound images were taken from the rectus femoris (RF) and the vastus lateralis (VL). All groups increased their RF (p < 0.001) and VL (p < 0.001) muscle thickness, while the increases in pennation angle were larger in HIT as compared to BFRT LV (p = 0.013) and BFRT HV (p = 0.037). These results support the hypothesis that acute muscle cell swelling may be involved in the processes underlying BFRT induced muscle hypertrophy. Furthermore, our data indicate differing structural responses to exercise between BFRT and HIT.
Discrepancies exist whether blood flow restriction (BFR) exacerbates exercise-induced muscle damage (EIMD). This study compared low-intensity eccentric contractions of the elbow flexors with and without BFR for changes in indirect markers of muscle damage. Nine untrained young men (18–26 y) performed low-intensity (30% 1RM) eccentric contractions (2-s) of the elbow flexors with one arm assigned to BFR and the other arm without BFR. EIMD markers of maximum voluntary isometric contraction (MVC) torque, range of motion (ROM), upper arm circumference, muscle thickness and muscle soreness were measured before, immediately after, 1, 2, 3, and 4 days after exercise. Electromyography (EMG) amplitude of the biceps brachii and brachioradialis were recorded during exercise. EMG amplitude was not significantly different between arms and did not significantly change from set 1 to set 4 for the biceps brachii but increased for the brachioradialis (p ≤ 0.05, 12.0% to 14.5%) when the conditions were combined. No significant differences in the changes in any variables were found between arms. MVC torque decreased 7% immediately post-exercise (p ≤ 0.05), but no significant changes in ROM, circumference, muscle thickness and muscle soreness were found. These results show that BFR does not affect EIMD by low-intensity eccentric contractions.
Abstract
Background
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.
Methods
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.
Results
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).
Conclusion
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.
