Effects of aging on human skeletal muscle after immobilization and retraining

Abstract

Inactivity is a recognized compounding factor in sarcopenia and muscle weakness in old age. However, while the negative effects of unloading on skeletal muscle in young individuals are well elucidated, only little is known about the consequence of immobilization and the regenerative capacity in elderly individuals. Thus the aim of this study was to examine the effect of aging on changes in muscle contractile properties, specific force, and muscle mass characteristics in 9 old (61-74 yr) and 11 young men (21-27 yr) after 2 wk of immobilization and 4 wk of retraining. Both young and old experienced decreases in maximal muscle strength, resting twitch peak torque and twitch rate of force development, quadriceps muscle volume, pennation angle, and specific force after 2 wk of immobilization (P < 0.05). The decline in quadriceps volume and pennation angle was smaller in old compared with young (P < 0.05). In contrast, only old men experienced a decrease in quadriceps activation. After retraining, both young and old regained their initial muscle strength, but old had smaller gains in quadriceps volume compared with young, and pennation angle increased in young only (P < 0.05). The present study is the first to demonstrate that aging alters the neuromuscular response to short-term disuse and recovery in humans. Notably, immobilization had a greater impact on neuronal motor function in old individuals, while young individuals were more affected at the muscle level. In addition, old individuals showed an attenuated response to retraining after immobilization compared with young individuals.

Effect of bimagrumab on thigh muscle volume and composition in men with casting‐induced atrophy

“…The 25% reduction in knee extension strength following casting was similar to previous observations 15, 27, 30. Muscle weakness following immobilization by a full‐length leg cast was mainly due to the marked decrease in the maximum voluntary force (neurogenic muscle activation) rather than loss of TMV 43.…”

“…In the study by Wall et al .,29 immobilization for 5 days induced muscle loss of ~3.5%, which increased to 8.4% when immobilization was extended to 14 days. While this magnitude of muscle loss can be recovered with little rehabilitation in healthy young men, it is difficult to overcome in elderly patients 14, 15, 16, 31…”

“…Compliance with increased dietary protein intake and regular intensive exercise training is highly variable and typically unsustainable 1, 13, 14. In addition, the ability to recover from atrophied skeletal muscles is attenuated with age even when combined with improved nutrition and exercise 14, 15, 16. These physiological and behavioural obstacles to optimal recovery of involuntary muscle loss have prompted innovative approaches to treatment.…”

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

“…A previous study showed that young men displaying muscle atrophy following 2 weeks of immobilisation regained both quadriceps MVC and muscle volume to reach baseline levels after 4 weeks of resistance training (Suetta et al, 2009). Our study shows that with resistive training performed in the early post-disuse phase recovery from a longer immobilisation period is possible in a shorter recovery timescale.…”

“…In a longer ULLS study which lasted 4 weeks and resulted in a 22% decrease in KE strength, muscle torque remained 11% below baseline levels after 4 days of passive recovery, eventually returning to normal 7 weeks following the ULLS period (Berg et al, 1991). Similarly, another study of 2-week immobilization showed that the KE torque could return to pre-ULLS levels within 4 weeks of active recovery (Suetta et al, 2009). The results of this study are noteworthy for they imply that early active recovery may not only improve patient functional status but is likely have a greater impact on quality of life, hereby reducing post-treatment hospitalisation times.…”