Limitations of concentration measurements for evaluation of endocrine status of exercising women.

The impact of changes in metabolic clearance rates (MCR), biologic activity of sex-steroids, steroid-protein interaction and steroid-binding properties of plasma proteins in relation to physical exercise are reviewed. The MCR of estradiol is decreased during physical exercise but this phenomenon is only partly explained by a decreased hepatic blood flow. Changes in concentration of high-affinity steroid binding proteins (testosterone-estradiol-binding globulin, TeBG) affect predominantly the amount of free testosterone (T) and its MCR. During exercise both the lower sex-steroids binding affinities of plasma proteins due to increased body temperature and the increased concentration of these hormones cause a shift towards an increased free concentration. Due to competitive interactions between androgens and estrogens for the binding site of TeBG the free concentration of estrogens will probably increase more than expected. The physiological meaning of these changes are discussed.