Physical exercise triggers neurons within the central nervous system which are responsible for complex alterations of the hypothalamo-pituitary axis as well as an increase in sympathoadrenal activity. Although mechanisms controlling the release of pituitary hormones have not yet been fully understood, there is evidence that endogenous opioid peptides and catechol oestrogens probably play an important neuromodulatory role. From the clinical point of view female reproductive function is exquisitely sensitive to physical training. However, cycle disturbances disappear spontaneously when training is drastically reduced. After cessation of sports activities, fertility and pregnancy do not seem to be affected. Growth delay is observed in some types of sport. It is similar to constitutional short stature and therefore probably not related to growth hormone secretion.