Bruce, Stuart Alexander; (1994) The effects of ageing and nutritional status on voluntary muscle function tests using human adductor pollicis muscle. Doctoral thesis (M.D), UCL (University College London).

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Abstract

Maximum voluntary force and cross-sectional area (CSA) of adductor pollicis muscle have been measured to examine the weakness associated with ageing and that associated with subnutrition, in six groups of subjects: 1) fit young, 2) fit elderly, 3) subnourished young, 4) elderly hip fracture patients, 5) post-menopausal women not receiving hormone replacement therapy, 6) post-menopausal women on hormone replacement therapy. In normally nourished young adults no sex difference was found in the force produced for a given cross-sectional area of adductor pollicis muscle. Likewise subnourished young adults produced the same force/CSA as their normally nourished counterparts. Pre-menopausal women and the subnourished produced lower forces but this was because they had smaller muscles. In contrast the elderly had a lower force/CSA. This reduction was particularly marked in those with osteoporotic fractures. As women are more prone to these fractures we predicted that a sex difference might be found with ageing and we have demonstrated this to be in the time-course of the decline in force/CSA. In women the decline was clearly related to the menopause. In men it was more gradual and its onset later. Possible causes for a low force/CSA are: 1) incomplete muscle activation - the force is not maximal. This was excluded in our weak elderly subjects using twitch interpolation. 2) replacement of the muscle with non-contractile tissue - the CSA is artefactually large. This was excluded by showing that the force obtained during stretch of the actively contracting adductor pollicis muscle is greater as a proportion of the isometric force in weak post-menopausal women than in young adults. This therefore suggests that the low force/CSA in these subjects is due to: 3) a change in cross-bridge function. Finally we found that the force/CSA in post-menopausal women is maintained by oestrogen replacement therapy suggesting that the change in cross-bridge function is hormonally mediated.

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