Ngambi Onambele, Gladys Leopoldine; (2002) Muscle strength control in women: Oestrogen, ACE and training effects. Doctoral thesis (Ph.D.), University College London.

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Abstract

The thesis describes the result of measuring force during voluntary contractions of the hand muscles, during stretch and in response to single magnetic stimuli. Measurements were made of muscle size and of handgrip strength in functional tasks. Groups of subjects studied included men, pre-menopausal women, post-menopausal women using HRT and those not using HRT. A follow up study was made of subjects from a previously published trial of HRT and observations were made of their ACE (angiotensin converting enzyme) genotypes. The in vivo effects of stretch velocity and activation level on the ratio of the force during stretch to that during isometric contraction (E/I) were investigated. All the female groups were studied before and after training of one hand. The benefits to muscle strength of HRT lasted several years even in those who stopped treatment after 1-2 years. The benefits of HRT were greater in those having one or more copies of the I form of the ACE gene compared to those homozygous for the D form. A stretch velocity >435 mm/sec is required for E/I to be independent of velocity. E/I is dependent on the isometric force (I) at the time of stretch and as activation level increases E/I decreases exponentially. Muscle strength of the trained hand, but not of the control hand, improved with training in all groups. The response to training was significantly greater in the postmenopausal women not taking HRT, compared to the other groups. Muscle strengthening occurred without significant size changes. There were no significant changes in the size of the interpolated twitches. The increase in strength caused by training was accompanied by a decrease in E/I following a relationship to I similar to that described for the changes in voluntary force development. There were marked improvements in hand function after training; these were likely due to a learning effect, since both trained and untrained hands showed similar effects. The implications of these findings are discussed.

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