The effect of sex hormones on skeletal muscle adaptation in females

Sex steroids, commonly referred to as sex hormones, are integral to the development and maintenance of the human reproductive system. In addition, male (androgens) and female (estrogens and progestogens) sex hormones promote the development of secondary sex characteristics by targeting a range of other tissues, including skeletal muscle. The role of androgens on skeletal muscle mass, function and metabolism has been well described in males, yet female specific studies are scarce in the literature. This narrative review summarises the available evidence around the mechanistic role of androgens, estrogens and progestogens in female skeletal muscle. An analysis of the literature indicates that sex steroids play important roles in the regulation of female skeletal muscle mass and function. The free fractions of testosterone and progesterone in serum were consistently associated with the regulation of muscle mass, while estrogens may be primarily involved in mediating the muscle contractile function in conjunction with other sex hormones. Muscle strength was however not directly associated with any hormone in isolation when at physiological concentrations. Importantly, recent evidence suggests that intramuscular sex hormone concentrations may be more strongly associated with muscle size and function than circulating forms, providing interesting opportunities for future research. By combining cross-sectional, interventional and mechanical studies, this review aims to provide a broad, multidisciplinary picture of the current knowledge of the effects of sex steroids on skeletal muscle in females, with a focus on the regulation of muscle size and function and an insight into their clinical implications. HighlightsFree testosterone, but not total testosterone, is associated with lean mass but not strength in pre- and post-menopausal females.Progesterone and estrogens may regulate muscle mass and strength, respectively, in females.Intra-muscular steroids may be more closely associated to muscle mass and strength, compared to systemic fractions.