Muscle size, neuromuscular activation, and rapid force characteristics in elderly men and women: effects of unilateral long-term disuse due to hip-osteoarthritis

Abstract

Suetta C, Aagaard P, Magnusson SP, Andersen LL, Sipilä S, Rosted A, Jakobsen AK, Duus B, Kjaer M. Muscle size, neuromuscular activation, and rapid force characteristics in elderly men and women: effects of unilateral long-term disuse due to hip-osteoarthritis. J Appl Physiol 102: [942][943][944][945][946][947][948] 2007. First published November 22, 2006; doi:10.1152/japplphysiol.00067.2006.-Substantial evidence exists for the age-related decline in muscle strength and neural function, but the effect of long-term disuse in the elderly is largely unexplored. The present study examined the effect of unilateral long-term limb disuse on maximal voluntary quadriceps contraction (MVC), lean quadriceps muscle cross-sectional area (LCSA), contractile rate of force development (RFD, ⌬force/⌬time), impulse (͐force dt), muscle activation deficit (interpolated twitch technique), maximal neuromuscular activity [electromyogram (EMG)], and antagonist muscle coactivation in elderly men (M: 60 -86 yr; n ϭ 19) and women (W: 60 -86 yr; n ϭ 20) with unilateral chronic hip-osteoarthritis. Both sides were examined to compare the effect of long-term decreased activity on the affected (AF) leg with the unaffected (UN) side. AF had a significant lower MVC (W: 20%; M: 20%), LCSA (W: 8%; M: 10%), contractile RFD (W: 17-26%; M: 15-24%), impulse (W: 10 -19%, M: 19 -20%), maximal EMG amplitude (W: 22-25%, M: 22-28%), and an increased muscle activation deficit (Ϫ18%) compared with UN. Furthermore, women were less strong (AF: 40%; UN: 39%), had less muscle mass (AF: 33%; UN: 34%), and had a lower RFD (AF: 38 -50%; UN: 41-48%) compared with men. Similarly, maximum EMG amplitude was smaller for both agonists (AF: 51-63%; UN: 35-61%) and antagonist (AF: 49 -64%; UN: 36 -56%) muscles in women compared with men. However, when MVC and RFD were normalized to LCSA, there were no differences between genders. The present data demonstrate that disuse leads to a marked loss of muscle strength and muscle mass in elderly individuals. Furthermore, the data indicate that neuromuscular activation and contractile RFD are more affected by long-term disuse than maximal muscle strength, which may increase the future risk for falls.aging; rate of force development; neural activity; muscle activation IT IS WELL KNOWN FROM ANIMAL and human studies that a chronic reduction in neuromuscular activity results in marked muscle atrophy (4, 28), reduced muscle strength (2, 33), and diminished neural drive to muscle fibers (9). For people older than 45 yr of age, Ͼ33% suffer from joint pain, and osteoarthritis (OA) has been shown to be the most common cause of inactivity and long-term disability in people aged Ն65 yr (12). However, most of the current knowledge with respect to the effects of inactivity and immobilization on neuromuscular function is based on animal data (2, 8) or on studies performed on healthy young individuals (4, 28). This is contrasted by the fact that the elderly population more often undergoes periods of immobilization and disuse, not only due to join...

Targeting Care

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