Circadian rhythm amplitude--is it related to rhythm adjustment and/or worker motivation?

Abstract

The results of two studies are presented, the first from subjects undergoing an irregular schedule of sleep and wakefulness in an isolation unit, the second from nurses during their normal night duty. In the first study, for individuals during the irregular schedule, there was some evidence for an inverse relationship between the amplitude and acrophase adjustment of the circadian rhythms of deep body temperature and urinary excretion of potassium, sodium and urate. No clear relationships between these variables were found either if group data from the subjects were considered or if the amplitude of circadian rhythms during conventional hours of sleep and wakefulness was compared with acrophase adjustment on the irregular schedule. In the second study there was evidence that nurses working at night on single occasions only continued a conventional diurnal routine as far as possible, whereas, when a number of consecutive nights were worked, there was evidence that substantial changes in routine, even encroaching upon leisure time, took place; this can be interpreted as ‘commitment’ on the parts of frequent night workers. The possible relationship between the amplitude of circadian rhythms and 'commitment' in shift workers is considered.