Plasma melatonin increases during exercise in women.

Melatonin was measured in plasma of seven women volunteers before and after serial acute submaximal exercise tests performed during the course of a two-month, progressive endurance training program. Plasma melatonin increased during all exercise sessions and declined towards baseline values when re-measured thirty minutes after completion of each exercise. This finding indicates that vigorous physical activity elicits transient increases in plasma melatonin in both sedentary and trained women.