Compensation of reduced sleep in a rapidly rotating shift system.

Sleep characteristics were examined in various phases of a forward rapidly rotating shift cycle in two groups of workers. In view of the fact that age is related to both sleep duration and the incidence of napping the relationships between sleep characteristics were analysed with age statistically held constant. The results showed that reduced sleep duration in one phase of the shift cycle (morning or night shift) was compensated by prolonged sleep in the following phase (afternoon shift and days off). Sleep was not prolonged equally for different workers; those sleeping shorter in the previous phase of the shift cycle prolonged their sleep more while those sleeping longer in the previous phase prolonged their sleep less. There was no relationship between the duration of the main sleep and the incidence of napping. The results are considered to be an additional argument in favour of the rapidly rotating shift system as compared to the permanent or slowly rotating shift systems.