・Physical exercise under bright light conditions is effective for phase-resetting of the circadian pacemaker and the sleep-wake cycle.

・Physical exercise under bright light conditions can prevent unavoidable sleep loss after jet-lag travel.

・Bright light is the primary synchronizer for the circadian pacemaker, as physical exercise is for the sleep-wake cycle.

Sleep-wake cycle in humans shows a precise rhythmicity with a period of 24 h. This rhythm is usually regulated by an internal circadian pacemaker, a.k.a., a biological clock. However, abrupt changes of social schedule (e.g. jet-lag) occasionally induce an internal desynchronization between the circadian pacemaker and external environmental schedule, which is thought to be a cause of jet-lag disorder.

The human circadian pacemaker entrains to a bright light more than 1,000 lux. Timed exposure to bright light can accelerate phase-resetting of the circadian pacemaker. Previously, we could demonstrate that timed physical exercise accelerates re-entrainment of the sleep-wake cycle after a phase-advance shift of sleep schedule in a temporal isolation facility; however, timed physical exercise did not influence the circadian pacemaker. As a result, we concluded that timed physical exercise alone cannot cancel the internal desynchronization between the circadian pacemaker and sleep-wake cycle.

In our present study, we demonstrated that physical exercise under bright light conditions accelerates reentrainment of the circadian pacemaker to the phase-advanced sleep schedule. This acceleration was not evident with exposure to bright light alone. Subsequently, we concluded that timed physical exercise under bright light conditions is important for accelerating the reentrainment of the circadian pacemaker. Although exposure to bright light is thought to have the same phase resetting potency when the exposure schedule is skillfully controlled, the present findings address that timed physical exercise under bright conditions can elicit phase-resetting potency of the circadian pacemaker without taking any labor.

Yujiro Yamanaka, Graduate School of Medicine, Assistant Professor, Hokkaido University

TEL: +81-11-706-5158

FAX: +81-11-706-7877

E-mail:y-yu2ro@med.hokudai.ac.jp

Department of Cell Physiology