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

¹Institute of Sports Medicine, Bispebjerg Hospital, University of Copenhagen, ²Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, and ³National Institute of Occupational Health, Copenhagen, Denmark; ⁴Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland; and Departments of ⁵Radiology and ⁶Orthopedics, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark

Submitted 19 January 2006 ; accepted in final form 10 November 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 = 19) and women (W: 60–86 yr; n = 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 (–18%) 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

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