Human Circadian Rhythms and the 48 Hour Day

Abstract

A COMMON approach to the understanding of human circadian rhythms is to study their modifiability. Attempts to replace the 24 h sleep–wakefulness rhythm in man by cycles of slightly altered length (for example, 21 or 27 h) have had some success^1,2. Attempts to produce sleeping–waking rhythms which are a multiple of the natural cycle length such as 12 or 48 h have not, however, been very successful^2,3; the reasons for this are not yet clear.