Circamensal rhythmicity and muscle function: The role of reproductive hormones in the regulation of strength

The human female menstrual cycle is characterised by fluctuations in reproductive and pituitary hormones which regulate the monthly release of an ovum for fertilisation. The circamensal changes in the hormonal milieu may influence exercise performance. The generation of maximal voluntary muscle strength, mediated by changes in the steroid hormones, has been the focus of recent research, particularly ergogenic effects of oestrogen. Peak force of the adductor pollicis, normalised for muscle size, has been reported mid-cycle in concert with the rise in oestrogen. The removal of an oestrogen and progesterone environment results in muscle weakness in humans and animals. These hormones decline concomitantly following natural ovarian failure (i.e., the menopause) and surgical extraction of the ovaries (i.e., bilateral oophorectomy). To overcome the problem of controlling for rapid cyclical changes in reproductive hormones across the menstrual cycle, and to isolate the effects of oestrogen when measuring strength, other models have been adopted. Treatment of in vitro fertilisation patients involves, in part, the down-regulation of gonadotropin releasing hormone receptors followed by upregulation with exogenous pituitary hormones. This presents a very low and very high oestrogenic milieu while progesterone remains relatively stable. Under these conditions, maximal strength of the first dorsal interosseus muscle has been unchanged. The rapid loss in strength observed post-menopause is preserved, and possibly restored, in women taking hormone replacement therapy. These findings are significant for the preservation of skeletal and muscular health of post-menopausal women. There is increasing evidence to support the role of reproductive hormones in the regulation of muscle strength. Since the link between the hormone milieu during the menstrual cycle and strength changes is weak, other models must be employed. Strength declines rapidly at the menopause, and offsetting muscle weakness in post-menopausal women has implications in reducing the risk of muscloskeletal injury. Female athletes who are prone to amenorrhoea constitute another target group. A hormone-deficient state may not be beneficial to performance, but may compromise muscle function.