[Human circadian rhythms and the work and rest regimen: the hypothesis of the "coiled spring"]

Studies of human free-running circadian rhythms have been reviewed. The conditions of development of free-run of the circadian rhythms were considered. On the basis of these data a hypothesis of "compressed spring" was proposed. It claims that the human circadian rhythms synchronized within the 24 h day are instable and related to physiologic tension. It follows that in conditions of relative isolation (long-term space flight, submarine navigation, polar expedition), during the transition period after a trans-meridian flight, and during adaptation to a shift (especially, night) work it is advisable to arrange a work-rest schedule on the basis of a prolonged 25 h day.