13 swimmers (mean age 14.8 ± 1.4; 46% male) and 19 rowers (mean age 16.5 ± 1.1; all male) wore actigraphs and completed sleep diaries over a 2-week training period. Diaries included the Hooper Index and a question regarding device use before bed. Participants also completed chronotype questionnaires. Nights of the week were categorised as taking place before "morning training", "mornings off", "weekend mornings off", and "weekend morning training". Actigraphy and sleep diary variables were compared for different nights of the week. Results All athletes were classified as "morning type". Average sleep duration across the study was 7h55 (±1h33). Median sleep duration was significantly shorter on nights before weekday morning training (6h44) compared to weekday mornings off (8h45). This was due to an earlier wake time (04:51) while bedtime remained constant (~22:15). Athletes went to bed later, woke later and slept for longer on nights before weekend mornings off compared to weekday nights. Conclusions Early morning training advanced the wake times of the athletes while bedtime remained constant. This shortened sleep below age recommended durations on the nights before early morning training during the week. These findings suggest that weekly average sleep duration does not accurately reflect athletes` nightly sleep given the large variability across a training week. Highlights • Sleep duration of adolescent athletes is reduced by early morning training. • Morning training (weekday and weekend) shortened sleep below age recommendations. • Sleep before mornings free of training fell within age recommended durations. • On weekends without training, adolescent athletes delay and extend their sleep. • Adolescent athletes use electronic devices in the hour before bed on 90% of nights.
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