Melatonin levels and exercise in adolescent boys and girls

Saliva concentrations of the indolamine melatonin were measured in adolescents of both genders who were typed as sedentary (only performing school physical activities) and sport-loving (school physical activity and at least 3 hours/week extracurricular exercise) after they had carried out an uninterrupted physical trial at an intensity between moderate (pulse-rate 120 beats/min) and submaximal (180 beats/min). Samples were collected before and after the physical trial and again at 23:00 h. The saliva melatonin levels were determined by radioimmunoassay. The results indicated that the sports girls presented higher melatonin levels than the sedentary girls in basal conditions, and that the physical trial raised these levels in both groups of girls. Extracurricular physical activity led to no differences in the basal melatonin levels between the two groups of boys, and there were no significant changes observed after the exercise trial in either group. The nocturnal levels of melatonin were the highest in all four groups.