Effect of physical exercise on plasma melatonin levels in normal volunteers

Plasma melatonin, cortisol and prolactin levels were determined in clinically normal adult Black male volunteers before, immediately after, and 1 hour after a period of controlled physical exercise. In all subjects the levels of these three hormones showed highly significant increases immediately after exercise and returned to pre-exercise levels 1 hour after physical exertion. In subjects who exercised in a room with reduced environmental lighting (54 lux), the plasma melatonin level immediately after exercise was significantly higher than in the group who exercised in a room with a lighting level of 320 lux. Reduction of environmental lighting had no effect on the plasma cortisol and prolactin values immediately after exercise. Significant positive relationships between post-exercise melatonin levels and body mass, age and pulse rate were noted in all volunteers. Since plasma melatonin reached a plateau level after 30 minutes, it is suggested that controlled exercise (step-climbing), which induces an energy output of 185 W/m2 body surface, conducted in a room with reduced environmental lighting for a period of 30 minutes, may form the basis for a pineal function test.