Objective: To assess and discuss the effects of exercise training on hormonal concentrations. Data sources: Papers were identified through MEDLINE (keywords: hormones and exercise, overreaching, overtraining). Study section and data extraction: The selected papers examined were from established sports sciences/ endocrine/ physiology journals, and specifically related to hormones and exercise. Conclusions: Optimal hormonal assessment requires that the physiological, technical and analytical variables that can influence the measured hormonal values are understood by those performing the interpretation of hormonal values. Knowledge of these factors will allow a better hormonal follow-up of athletes, and a higher efficiency in detecting and preventing abnormal fatigue and the overtraining syndrome (OTS), as well as preventing hormonal doping.