Abstract
The time of day (TOD) has a significant influence on physical performance through circadian rhythms, which regulate body temperature, muscle function, and hormone levels. While extensively studied in adults, the impact of TOD on adolescent athletes remains underexplored. This study aimed to investigate the effects of TOD on maximal short-term physical performance in adolescent soccer players, to guide evidence-based decisions regarding the structuring of training and competition schedules. Nineteen male adolescent soccer players (mean age: 14.58 ± 0.7 years) participated in a randomized trial, performing at four TOD sessions (08:00 h, 11:00 h, 15:00 h, and 18:00 h) with recovery periods of at least 48 hours between sessions. Performance metrics included oral temperature (OT), medicine ball throw (MBT), 5-meter sprint (5m-T), 20-meter sprint (20m-T), Illinois Agility Test (IAT), and Illinois Agility Test with Ball (IAT-B). Results revealed significant TOD effects. OT increased notably from 08:00 to 18:00 (p < 0.001). Physical performance metrics (MBT, 5m-T, 20m-T, IAT, and IAT-B) improved significantly at 11:00, 15:00, and 18:00 (all p < 0.05) relative to 08:00. The 18:00 session consistently produced the highest performance levels. At the same time, no significant differences were observed between 11:00 and 15:00 (all p > 0.05). Our results suggest that time of day significantly influences short-term maximal physical performance in adolescent male soccer players, with peak performance levels consistently observed in the late afternoon (18:00 h). This appears to reflect diurnal variations in core temperature, hormonal activity, and neuromuscular readiness, which likely enhance sprint speed, agility, and explosive power at this time. These findings indicate that coaches and youth sport practitioners should consider scheduling high-intensity training sessions and performance assessments in the late afternoon to optimize physiological conditions for training and evaluation. Aligning training and competition timing with circadian rhythms may therefore support improved athletic output and more accurate performance monitoring in youth soccer settings.