Hvid, L. G., Suetta, C., Nielsen, J. H., Jensen, M. M., Frandsen, U., Ortenblad, N., Kjaer, M., & Aagaard, P. (2014). Aging impairs the recovery in mechanical muscle function following four days of disuse. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 2225.

This study investigated the effect of four days lower limb disuse followed by seven days of active recovery on mechanical muscle function in young (N = 11; ~ 24.3 years) and older (N = 11; ~67.2 years) recreationally active healthy males. Isometric and dynamic knee extensor strength was assessed using isokinetic dynamometry. Contractile rate of force development and impulse were obtained in the initial contraction phase (0-100 ms relative to onset of contraction).

Age-related differences (young greater than older group) were observed at baseline in isometric and dynamic muscle strength (~35%), rate of force development, and impulse (~39%). Both groups showed significantly comparable decrements with disuse in isometric strength (~9%), slow speed (30°/s) dynamic strength (~13%), rate of force development (~19%), and impulse (~19%). The older group showed additional reductions in fast speed (160°/s) dynamic strength (12%), and relative rate of force development (~17%). Following recovery (including two resistance training sessions), mechanical muscle function was fully restored in the young group, whereas isometric and dynamic muscle strength remained reduced in the older group (~8%).

Implication. Short-term (four days) lower limb disuse causes marked decrements in mechanical muscle function in both young and older men, with older men demonstrating greater relative decrements in dynamic strength and rate of force development. Short-term (seven days) active recovery fully restored mechanical muscle function in young men, while sustained impairments in isometric/dynamic muscle strength were observed in older men (representing elevated risk factors for falls). Short-term disuse in elderly males requires longer periods of active recovery to remove persisting impairments in mechanical muscle function.

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