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1 Bispebjerg Hospital, University of Copenhagen, Institute of Sports Medicine, Denmark
2 University of Southern Denmark, Institute of Sports Science and Clinical Biomechanics, Odense, Denmark; Bispebjerg Hospital, University of Copenhagen, Institute of Sports Medicine, Denmark
3 University of Copenhagen, National Institute of Occupational Health, Copenhagen, Denmark
4 4Department of Health Sciences, University of Jyvaskyla,, Finland
5 Bispebjerg Hospital, University of Copenhagen, Dept. of Radiology, Denmark
6 Bispebjerg Hospital, University of Copenhagen, Dept. of Orthopedics, Denmark
* To whom correspondence should be addressed. E-mail: cs08{at}bbh.hosp.dk.
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 (ITT), maximal neuromuscular activity (EMG) and antagonist muscle co activation in elderly men (M:60-86yrs, n=19) and women (W:60-86yrs, n=20) with unilateral chronic hip-osteoarthritis. Both sides were examined to compare the effect of long-term decreased activity on the affected leg (AF) with the unaffected side (UN). 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 to UN. Furthermore, women were less strong (AF:40%; UN:39%), had less muscle mass (AF:33%; UN:34%) and a lower RFD (AF:38-50%; UN:41-48%) compared to men. Likewise, 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 to 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.
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