Effects of aging on muscle mechanical function and muscle fiber morphology during short-term immobilization and subsequent retraining

Abstract

Very little attention has been given to the combined effects of aging and disuse as separate factors causing deterioration in muscle mechanical function. Thus the purpose of this study was to investigate the effects of 2 wk of immobilization followed by 4 wk of retraining on knee extensor muscle mechanical function (e.g., maximal strength and rapid force capacity) and muscle fiber morphology in 9 old (OM: 67.3 ± 1.3 yr) and 11 young healthy men (YM: 24.4 ± 0.5 yr) with comparable levels of physical activity. Following immobilization, OM demonstrated markedly larger decreases in rapid force capacity (i.e., rate of force development, impulse) than YM (∼ 20-37 vs. ∼ 13-16%; P < 0.05). In contrast, muscle fiber area decreased in YM for type I, IIA, and IIx fibers (∼ 15-30%; P < 0.05), whereas only type IIa area decreased in OM (13.2%; P < 0.05). Subsequent retraining fully restored muscle mechanical function and muscle fiber area in YM, whereas OM showed an attenuated recovery in muscle fiber area and rapid force capacity (tendency). Changes in maximal isometric and dynamic muscle strength were similar between OM and YM. In conclusion, the present data reveal that OM may be more susceptible to the deleterious effects of short-term muscle disuse on muscle fiber size and rapid force capacity than YM. Furthermore, OM seems to require longer time to recover and regain rapid muscle force capacity, which may lead to a larger risk of falling in aged individuals after periods of short-term disuse.

Neuromuscular electrical stimulation increases muscle protein synthesis in elderly type 2 diabetic men

“…Importantly, this is the first study to show that NMES directly stimulates skeletal Disuse muscle atrophy can contribute significantly to the loss of muscle with aging. Elderly individuals have been reported to lose substantial amounts of muscle tissue during only short periods of muscle disuse (17,21,44) and generally show a reduced ability to regain muscle tissue lost during subsequent rehabilitation (34,61). Furthermore, elderly type 2 diabetes patients commonly have an accelerated loss of muscle mass when compared with healthy elderly individuals (53).…”

Strength training-induced responses in older adults: attenuation of descending neural drive with age

“…Although the isometric training may also account for some of the adaptations, these studies together present mounting evidence that heavy resistance training not only is feasible and effective; additionally, no incidents of injury have been reported. Importantly, the large improvements in RFD in these studies, typically between 50 and 150 %, will imply a clear risk reduction for falls (Hvid et al 2010). Considering the importance of muscle strength and rapid force development in particular (Fleming et al 1991;Izquierdo et al 1999;Suetta et al 2007;Aagaard et al 2010), the neuromuscular deterioration certainly represents a challenge in order to maintain high physical functionality at old age.…”

“…Indeed, this is an important aspect since it also reflects the changes of the fast twitch muscle fibers, which are closely linked to balance adjustments and fall prevention (Hvid et al 2010). The V-wave methodology, an electrophysiological variant of the H-reflex technique, evoked in the triceps surae muscles during maximal muscle contraction has been applied for this frame of testing in several studies (Upton et al 1971;Aagaard et al 2002;Duclay and Martin 2005;Fimland et al 2009;Ekblom 2010;Fimland et al 2010;Fimland et al 2011;Vila-Cha et al 2012).…”

Impaired skeletal health and neuromuscular function among amphetamine users in clinical treatment

“…The muscle strength reductions among the amphetamine users correspond to what is typically observed at 30-40 years of age [38], and are closely linked to fall and fracture risk [39], every day physical function [39,40], and even all-cause mortality [22]. The observed reductions in muscular strength and bone mass may be influenced not only by the amphetamine use, but could also be a result of inactivity.…”