O017 Training schedules and light as synchronisers of athlete circadian rhythms

Abstract Introduction Sleep and circadian rhythms can be harnessed for recovery and performance. Seasonal scheduling in elite sports likely influences zeitgeber timing. Yet, the effect of seasonal scheduling on athlete circadian biology is unknown. This study investigated differences in sleep and circadian biology during pre-season and in-season among elite athletes. Methods Elite professional male Australian Rules footballers (n = 52; M-age = 24.37 years), in two consecutive years, were observed for two weeks during pre-season (early morning training; summer) and two weeks during in-season (no early morning training; winter), resulting in 164 participant datasets. Sleep and light exposure were measured using actigraphy. Circadian phase was measured using dim light melatonin onset. Furthermore, a healthy control sample was used to explore athlete seasonal changes in circadian phase relative to non-athletes. Timing variables were transformed to standard time. Results Relative to in-season, pre-season mid-sleep (-93 mins), circadian phase (-110 mins) and bright light onset (-139 mins) were significantly advanced, and pre-season sleep duration was shorter (-17 mins). Timing of bright light exposure onset partially mediated the effect of season on mid-sleep and circadian phase. Exploratory analyses revealed that the athlete circadian phase advance in pre-season was uniquely larger relative to the non-athlete advance (-67 mins) in summer. Discussion Early morning training periods, and the associated earlier light exposure, significantly advance circadian biology in elite athletes. Training schedules, together with associated zeitgebers (light, exercise, diet etc), may be important synchronisers of athlete circadian clocks. Sports practitioners may consider training timing to optimise circadian influences on recovery and performance.