Synchronization effects of physical exercise on human peripheral clocks regulating behavior rhythms

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To clarify whether physical exercise is a time cue for the human circadian clock and the mechanism by which physical exercise entrains the clock, we performed a series of experiment under temporal isolation using an 8h phase-advanced desynchrony protocol. Adult female subjects were required to perfome physical exercise of 2 hour duration twice a day using bicycle ergometer. The circadian rhythms in plasma melatonin and deep body temperature, which are believed to be regulated by the central circadian pacemaker, were measured simultaneously with the sleep-wake cycle which is thought to be driven by the peripheral clock. As a result, the re-entrainment of the sleep-wake cycle to a 8 h phase-advanced schedule was accelerated by timed physical exercise under dim light of ca. 10 lx, whereas the plasma melatonin did not phase-advance regardless of timed physical exercise. On the other hand, the re-entrainment of the sleep-wake cycle was accomplished regardless of timed physical exercise under bright light of ca. 5,000 lx, whereas the plasma melatonin rhythm phase-advanced but did not fully entrain but phase-advanced with or without timed physical exercise. The findings indicate that time physical exercise has a potency to entrain the sleep-wake cycle, but the effect is masked under bright light conditions.