Napping, Caffeine, and Their Combination Enhanced Explosivity and Repeated-Sprint Performance: A Randomized Placebo-Controlled Study

The study aimed to examine the independent and combined effects of a 90-min early afternoon (12:30 p.m.) nap (NAP) and an early evening (6:00 p.m.) moderate dose of caffeine (CAF; 5 mg/kg) on afternoon's variation of subjective sleepiness and reaction time and evening (7:00 p.m.) physical performance. In a randomized, counterbalanced, and double-blind design, 13 physical education students completed four conditions separated by 3-7 days: placebo (PLA), NAP, CAF, and combined nap plus caffeine (NAP + CAF). Assessments included simple and choice reaction times and the Epworth Sleepiness Scale at 12:30 p.m., before napping/resting, and every hour between 3:00 p.m. and 7:00 p.m. Jumping performance (squat jump and countermovement jump) and the repeated modified agility test were assessed once at 7:00 p.m. No significant effects of CAF, NAP, and CAF + NAP on simple reaction time, choice reaction time, and Epworth Sleepiness Scale were found. Repeated modified agility test performance improved across all interventions compared with PLA, with no difference between interventions. All interventions enhanced squat jump performance relative to PLA, with the greatest improvements observed under NAP + CAF compared with CAF (p < .05, d = 0.37, mean difference MD = 1.92 cm; p < .05, d = 0.38, MD = 0.07 m/s; p < .05, d = 0.01, MD = 0.01 W/kg) and NAP (p < .01, d = 0.63, MD = 2.91 cm; p < .01, d = 0.68, MD = 0.11 m/s; p < .01, d = 0.02, MD = 0.02 W/kg), respectively, for squat jump, take-off velocity, and relative power. Napping and caffeine independently enhanced repeated agility and explosivity performances, and their combination had no additional benefits on repeated agility. However, the combination further enhanced explosivity, which may benefit evening competitions in team and racket sports. Its limited effects on nonexplosive tasks and potential sleep disruption constrain broader application.