Delaying Early Morning Training Time in Swimmers: Effects on Sleep, Recovery and Performance—A Randomized Controlled Trial

BACKGROUND: Swimmers often fail to achieve recommended sleep durations. Early morning training, common in swimming, is associated with shorter sleep. Sleep extension through later wake-up times appears to be an appropriate measure to counteract this. Therefore, this study investigated whether delaying early morning training has an effect on sleep, recovery and performance, and whether changes in sleep mediate eventual effects on recovery and performance. METHODS: Using cross-over design, 27 national-level swimmers (13 females, 14 males; age: 15.6 ± 1.0 years) completed two 8-day training camps in January and October 2023 in Saarbrücken, Germany. Morning sessions started at 07:00 AM (early) or 09:00 AM (late), with conditions randomized between camps. Sleep and recovery were assessed using actigraphy, sleep diaries, and the Short Recovery and Stress Scale. Performance was evaluated using 100 m main stroke and 800 m freestyle time-trials pre- and post-camp. Linear mixed-effects models and repeated measures analysis of variance were employed to assess the effect of training time on sleep, recovery and performance. Regression-based mediation analysis tested whether changes in sleep and recovery mediated the effects of training timepoint on recovery and performance. RESULTS: Sleep duration per night was significantly longer in the late compared to the early condition (1.0 ± 0.5 h; t = 14.0, p < .001). However, there was no significant effect on measures of recovery (p > .080), and 100 m and 800 m performance (p > .204). Mediation analysis showed no indirect effects of sleep duration on mental capacity or of mental capacity on performance (p > .05). CONCLUSION: Delaying early morning training from 07:00 AM to 09:00 AM increased sleep duration by one hour on average, but this did not significantly affect recovery or performance in elite swimmers. Nevertheless, the study provides evidence that early morning training is associated with reduced sleep duration and highlights the persistent sleep challenges faced by adolescent swimmers. Trial registration DRKS, DRKS00039267. Registered 17 February 2026-Retrospectively registered, https://www.drks.de/DRKS00039267 .