The body clock and athletic performance

Abstract

Athletes train and compete at different times of the day according to personal preferences, schedule of team training or timing of competition. Many human performance variables follow the circadian rhythm in physiological measures, in phase with the rhythm in core body temperature. This correspondence applies to components of performance, physiological determinants of performance with high power output, psychophysical loading and competitive time trials. There is evidence that circadian rhythms in exercise performance are, in part, endogenously driven. Human performance rhythms are disrupted when athletes travel rapidly across multiple meridians, or are engaged in nocturnal shift-work. Few sports participants maintain high-performance standards when operating shift-work regimens. In contrast, travelling across time-zones is a contemporary feature of competitive sport for sojourns and training camps and participating in international contests. Athletes like all travellers experience jet lag symptoms when crossing multiple time-zones. Symptoms are worse and last longer following flights to the east compared to flying westwards. Performance rhythms re-adjust to the new local time at about the same time as that of core temperature. Experience with Olympic athletes travelling between Europe and Australia is that adjustment may be by phase advance or phase delay depending on timing of departure and disembarkation, time of arrival and exposure or avoidance of natural light, and activity in the early days in the new time-zone. Adjustment can be assisted by means of a behavioural strategy that combines the body clock and the homeostatic drive to sleep. Exclusion of long naps, the diurnal timing of physical training and social events form part of this strategy, as do eating and drinking behaviour. Exercise is a potential resynchronising agent when utilised at the correct time of day. Pharmacological treatments, including use of melatonin, have found favour in some contexts but their phase response curves pose difficulties for their administration in athletes travelling on long-haul flights. In view of the national governing bodies' stances on use of pharmacological agents and supplements by athletes, the behavioural strategy to cope with jet lag has been advocated.

Keywords:

• circadian rhythm
• jet lag
• melatonin
• sleep
• travel