O067 The role of biological sex in the relationship between circadian alignment and well-being in elite athletes

INTRODUCTION: Circadian rhythms govern physiological timing and influence sleep, well-being, and performance. Desynchrony between circadian timing and behaviours (circadian misalignment) can compromise daily functioning. We investigated sex differences in sleep and circadian timing, and their relationship with sleep and mental health outcomes in elite athletes. METHODS: Participants were 87 elite Australian Rules Football (AFL) athletes (43% female; M-age =23.8±4.0 years). Data were collected prior to the start of the 2021 and 2022 AFL seasons (n= 54 participating in a repeat assessment). Circadian phase was assessed via salivary DLMO (collected hourly from 5hrs pre- to 1h post-habitual bedtime). A questionnaire battery, and two weeks of actigraphy were also completed. RESULTS: Female athletes had a significantly later circadian phase (DLMO; 20:42 vs 20:13) and midsleep time (03:24 vs 02:58), and worse self-reported athlete psychological strain (APSQ), daytime sleepiness, and insomnia, relative to male athletes. There was no sex difference in phase angle (interval between sleep onset and DLMO times; M = 2.5hrs ± 49 mins). DLMO time did not predict sleep efficiency, sleep latency, insomnia, sleepiness, or APSQ. Phase angle predicted APSQ for female athletes only, via a quadratic trend (p=.001): psychological strain was worse among female athletes with shorter and longer phase angles. DISCUSSION: Our results suggest female athletes have a later circadian phase, which is not associated with adverse outcomes except for higher psychological strain for those with greater circadian misalignment. Sports practitioners may require specific attention for circadian alignment in female athletes who are at particular risk when misaligned.