Sleep duration, timing, and regularity during school, training, and holiday periods in male adolescent soccer players.

Sleep is essential for adequate physical recovery and performance, but adolescent athletes face unique challenges that can disrupt sleep. Thus, this observational study aimed to monitor sleep in highly trained male adolescent soccer players between three distinct periods: (1) concurrent school and training; (2) morning training only (during the school winter break); and (3) a full holiday period (with no school or training) and assess the influence of morning alarm use on the differences between periods. Thirty-four male academy soccer players (16.6 ± 0.9 years) were monitored for five weeks using wrist-worn actigraphy and daily sleep diaries. Sleep outcomes included time in bed (TIB), total sleep time (TST), sleep timing, and the Sleep Regularity Index (SRI). Linear mixed-effects models were used to compare sleep variables across periods and to test interactions with morning alarm use. Mean sleep duration across the monitoring period was 06:47 ± 01:10 h, with none of the participants achieving the recommended minimum of 8 h of daily sleep. TIB and TST were slightly lower during the training-only period compared with the other periods (- 18 to - 31 min; trivial to small effects). Holidays were characterized by substantially later bedtimes (~ 1.5-2 h; moderate effects) and wake-up times (~ 2 h; moderate effects), without a meaningful increase in sleep duration (3 to 21 min; trivial effects). Marked differences in SRI were observed between periods (moderate to large effects), with higher SRI during structured periods and the lowest regularity during holidays (moderate to large effects). Not using an alarm resulted in longer TIB (+ 87 min; large effects) and TST (+ 66 min; moderate to large effects), particularly during holidays. The main results highlight that highly trained male adolescent soccer players had later sleep timing during holidays, which did not necessarily promote longer sleep; instead, it was associated with reduced sleep regularity. Moreover, morning alarm use negatively influenced sleep opportunity.