Chronobiology and sports performance

Chronobiology is the scientific study of biological rhythms which embraces ultradian, circaseptal, circamensal and seasonal rhythms as well as circadian aspects. Circadian rhythms refer to recurring biological cycles over each solar day. Body temperature is regarded as a fundamental variable, having a very strong endogenous component. There is evidence that many human performance measures vary throughout the day in close phase with the temperature curve. Exceptions apply to endurance performances and exercise in high ambient temperatures.
The time of day in which sports events are held therefore may influence the quality of performance. There are considerations also for safety and effectiveness of training. Circadian influences are most obvious when underlying rhythms are disturbed, such as in nocturnal shiftwork, sleep deprivation or desynchronisation of rhythms following long-haul flights.
Contemporary elite athletes travel regularly across multiple time zones, for purposes of training or competition. Such itineraries induce travel fatigue, including jet lag when multiple time zones are crossed. Jet-lag refers to a syndrome or cluster of symptoms that reflect desynchronisation of the normal circadian rhythm. Until rhythms are re-synchronised to harmonise with the new local time, performance may be compromised (Reilly et al., 1997).
Jet-lag is more severe and lasts longer the more time-zones that are crossed. Circadian resynchronisation is faster after travelling westwards compared to travelling eastwards. In order to hasten the adjustment to the new local time, the traveller may choose between pharmacological and behavioural strategies. The former includes benzodiazepines, central nervous system stimulants, melatonin, caffeine and other putative chronobiotics. The latter includes alterations of the sleep-wake cycle prior to travelling, but a behavioural strategy must be geared towards the direction of flight, the number of time zones crossed and the time of arrival in the new time zone. Experience of previous long-haul flights seems to provide opportunity for developing appropriate means of coping with jet-lag.

References

Reilly, T., Atkinson, G. and Waterhouse, J. 1997). Biological Rhythms and Exercise. Oxford: Oxford University Press.