Intramuscular sex steroid hormones are reduced after resistance training in postmenopausal women, but not affected by estrogen therapy.

Animal and human studies suggest that low concentrations of circulating sex steroid hormones play a critical role in the accelerated loss of muscle mass and strength after menopause. The skeletal muscle can produce sex steroid hormones locally, however, their presence and regulation remain mostly elusive. The purpose of this study was to examine sex steroid hormone concentrations in skeletal muscle biopsies from postmenopausal women before and after 12-weeks of resistance training with (n = 15) or without (n = 16) estrogen therapy, and after acute exercise. Furthermore, associations between circulating sex hormones, intramuscular sex steroid hormones and muscle parameters related to muscle strength, mass and quality were elucidated. Blood and muscle samples, body composition (DXA-scan), muscle size (MR), and muscle strength measures were determined before and after the intervention. An additional blood and muscle sample was collected after the last resistance exercise bout. The results demonstrated reduced intramuscular estradiol, testosterone and dehydroepiandrosterone (DHEA) concentrations after resistance training irrespective of estrogen therapy. Acute exercise had no effect on intramuscular sex hormone levels. Low circulating levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) associated with high muscle mass at baseline, and a decline in circulating FSH after the intervention associated with a greater gain in muscle cross-sectional area in response to the resistance training. In conclusion, intramuscular estradiol, testosterone and DHEA were reduced by resistance training and unaffected by changes in circulating estrogen levels induced by estrogen therapy. Serum FSH and LH were superior predictors of muscle mass compared to other circulating and intramuscular sex steroid hormones.