Adjustment of the oral temperature rhythm to a fixed watchkeeping system on board ship.

Oral temperature data were collected from 12 members of the crew of an oil tanker at sea. Most of the personnel examined were engaged on watchkeeping duties on a '4 on, 8 off' fixed-hours system; the remainder included 3 "day-workers". The study commenced after the subjects had been following their particular work schedules continuously for several weeks, thus providing good opportunity for adaptation to them. Observations were made at 4-hourly intervals during waking hours, over a period ranging from 8 to 13 days in individual cases. The form of the mean curves produced by averaging the readings over all days indicated that a reasonable degree of adjustment of the temperature rhythm to the different sleep/wake routines imposed by the work system had occurred. Estimates of rhythm phase and amplitude obtained by "single cosinor" time series analyses of the sequential data supported this impression. However, further investigations are needed to substantiate these findings, and also to determine how long it takes for the rhythm adjustment process to reach completion in inexperienced workers.