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Abstract Thirty-one subjects were employed in an experiment to determine whether the relationship between efficiency at mental tasks and the circadian rhythm of body temperature observed in an earlier study was affected by an increase in the length of the duty-spell from 4 to 8 hours. Subjects wore assigned either to a control ‘ day ’ shift (O800–1600), a ‘ night ’ shift (2200–0600) or a ( morning ) shift (0400–1200), and were tested for a period of 12 consecutive days on the same shift. The control shift-workers showed no consistent effects of fatigue due to the increased length of the duty-spell. Adaptation of temperature rhythm to work on the night shift was only partial, but was relatively closely reflected in the recorded performance trends. Very little adaptation to work on the morning shift was observed, and performance was thought to have been affected by partial sleep deprivation. It was concluded that body-temperature was as effective a predictor of overall mental efficiency in most industrial-type shifts as in the special 4-hour shift system previously investigated.
Colquhoun et al. (Fri,) studied this question.