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Maximum voluntary force and cross-sectional area (MVF and CSA) of the human adductor pollicis muscle were compared in groups of young (19-55 years, mean = 28, n = 53) and elderly (74-90 years, mean = 80, n = 39) subjects, of both sexes. Despite the elderly subjects being in good health and active outdoors, they were considerably weaker than the young subjects, their MVF/CSA being 26 +/- 3% (mean +/- SEM) lower. It was found that both young and elderly subjects could fully activate their muscles. Therefore the muscle weakness of old age does not appear to be due to reduced activation and must be caused by another mechanism, possibly biochemical in nature.
Phillips et al. (Sun,) studied this question.