STUDY OBJECTIVES: To examine the effect of the timing of high-intensity exercise (afternoon vs. evening) on adolescent athletes' bedtime psychological state, sleep quality, sleep staging, and next-day wellness/sleepiness according to chronotype.
METHODS: Forty-two young athletes (morning type: n = 12, intermediate type: n = 14; evening type: n = 16) completed a randomized crossover study under free-living conditions. The counterbalanced sessions include: (AEX) afternoon (1:00-3:00 p.m.) and (EEX) evening (5:30-7:30 p.m.) high-intensity exercise. Sessions were conducted over three days each and were separated by a 1-week washout period. The time in bed was fixed (10:30 p.m.-7:30 a.m.). Sleep was assessed through ambulatory polysomnography.
RESULTS: The effect of high-intensity exercise on sleep differs significantly depending on the time of exercise with lower sleep efficiency: SE (-1.50%, p < .01), and higher SOL (+4.60 min, p ≤=< .01), during EEX vs. AEX. Contrary to the previous view, we discovered differences in the mediated response based on the chronotype of young athletes. These differences were observable in the psychological state at bedtime, objective sleep, and the next day's self-reported wellness. Whereas the sleep of participants with a late chronotype remains stable regardless of the time of exercise, those with an early chronotype experience higher mood disturbances and clinically significant sleep disruptions following evening high-intensity exercise.
CONCLUSIONS: Exercise timing and chronotype affect the psychological state at bedtime and objective sleep in adolescent athletes. This also alters next morning signs of pre-fatigue and wellness which suggest that the consideration of both features is important to adolescent athletes' recovery.
