Physical exercise accelerates re-entrainment of human sleep-wake cycle but not of plasma melatonin rhythm to 8 h phase-advanced sleep schedule.
Effects of timed physical exercise were examined on the re-entrainment of sleep-wake cycle and circadian rhythms to an 8 hour phase-advanced sleep schedule. Seventeen male adults spent 12 days in a temporal isolation facility with dim light conditions. The sleep schedule was phase-advanced by 8 hours from their habitual sleep times for 4 days, which was followed by a free-run session for 6 days where the subjects were deprived of time cues. During the shift schedule, the exercise group (n=9) performed physical exercise with a bicycle ergometer in the early and middle waking period for 2 hours each. The control group (n=8) sat on a chair at those times. Their sleep-wake cycles were monitored everyday by polysomnography and/or weight sensor equipped with a bed. The circadian rhythm in plasma melatonin was measured on the baseline day before phase-shift, on the 4th day of shift schedule and the 5th day of free-run. As a result, the sleep-onset on the first day of free-run in the exercise group was significantly phase-advanced from that in the control and from the baseline. On the other hand, the circadian melatonin rhythm was significantly phase-delayed in the both groups, showing internal desynchronization of the circadian rhythms. The sleep-wake cycle resynchronized to the melatonin rhythm by either phase-advance or -delay shifts in the free-run session. These findings indicate that the re-entrainment of the sleep-wake cycle to a phase-advanced schedule occurs independent of the circadian pacemaker and is accelerated by timed physical exercise.