Circadian Performance Rhythms: Experimental Studies in Air Operations

Abstract

Aircrews operate round the clock and over many time zones. This implies interference of air operations with circadian oscillation of biological functioning as well as its disruption through shifts of environmental time cues. In this sense the significance of circadian performance rhythms in air operations is discussed. This is done mainly by presenting results from seven experimental studies in which behavioural and physiological variables were evaluated before and after transmeridian flights.

In general, performance was assessed every second post-flight day in three hourly intervals round the clock. Between midnight and 0900 hours subjects were allowed to sleep but were aroused twice for testing for a period of 45 minutes. In all but one study eight healthy male students in the range of 23 to 28 years of age served as subjects; in one experiment ten pilots participated in flight simulator tests.

The results confirmed the idea that alertness, or the readiness to be mentally active, belongs to these biological properties of the living organism which are subject to circadian variation. This rhythm persists after transmeridian flights and is de- and resynchronized with the environmental time cues similar to other biological cycles. It so happens that a low performance output temporarily occurs in the local daylight phase instead of, as usual, during the dark phase. Results given in the pertinent literature reveal an alternating effect on performance of operationally induced fatigue and the circadian rhythm; this interference is of operational significance.

Recommendations ave given for flight scheduling considering circadian rhythm effects.