Daytime exercise speeds up shifts in the human internal body clock

Plasma melatonin rhythm was significantly phase advanced with physical exercise during a 15-day forced sleep-wake schedule.

• The study involved subjects adhering to a forced sleep-wake schedule of 23 hours and 40 minutes over 12 cycles.
• Physical exercise was imposed twice per waking period for 2 hours each, using bicycle- or rowing-type ergometers.
• After 6 days of exercise, a significant phase advancement in melatonin rhythm was observed.
• The amplitude of the melatonin rhythm remained unchanged regardless of exercise.
• Exercise in the afternoon or at midnight caused a significant phase delay in melatonin rhythms compared to the prepulse phase.
• Phase shifts from exercise were not different from those observed in sedentary controls.

Simplified