Reilly, T., & Marshall, S. (1991). Circadian rhythms in power output on a swim bench. Journal of Swimming Research, 7, 11-13.

Circadian variation in power output (as performed on a biokinetic swim bench) and its relation to circadian rhythms in body temperature and subjective alertness were measured in 14 competent swimmers at six equidistant times (starting at 2:00 hr) of the day. Peak and mean power on a 30 s test were noted. Subjective scale responses for alertness and pre-exercise rectal temperatures were recorded.

Distinctive circadian rhythms for pulse rate, rectal temperature, alertness, and both power measures were exhibited. The general time for the peak values was after 16:00 hr. The difference between the highest and lowest values in the rhythm was 14% for mean power and 11% for peak power.

It was suggested that the amplitude of circadian rhythms increases with the complexity of motor tasks because of the size of the values obtained.

Implication. The circadian rhythm in power output on a swim bench was closely related to the rhythm for body temperature and alertness. The existence of these rhythms should be taken into account when planning strength and power training stimuli.

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