Effects of sleep restriction on cognitive and physical performance in elite karate athletes: A randomized crossover study

Background: Sleep deprivation negatively impacts athletic performance; however, limited research has specifically examined these effects in combat sports athletes, where rapid decision-making and neuromuscular coordination are crucial for success. This study aimed to investigate the impact of partial sleep restriction on cognitive and physical performance in elite karate athletes. Methods: Fourteen international-level male karate athletes (age: 23.35 ± 4.61 years) completed 2 randomized experimental sessions separated by 1 week: following regular sleep (8 hours) versus sleep restriction (4 hours). Cognitive performance was assessed using the Stroop test, simple reaction time, and multiple-choice reaction time tests. Physical performance was evaluated through the squat jump, modified agility T-test (MAT), and karate-specific aerobic test. Results: All tests were conducted before and after exercise. Sleep restriction significantly impaired cognitive performance. Stroop reaction times increased under sleep restriction ( F = 13.0, P <.01, ηp 2 = 0.50) with further deterioration post-exercise ( F = 60.27, P <.001, ηp 2 = 0.90). Simple reaction time declined following sleep restriction ( F = 27.2, P <.001, ηp 2 = 0.70). Multiple-choice reaction time remained unaffected at rest but worsened significantly after exercise ( F = 5.3, P <.05, ηp 2 = 0.30). Physical performance also declined: squat jump height decreased ( F = 15.8, P <.001, ηp 2 = 0.50), MAT performance deteriorated ( F = 28.5, P <.001, ηp 2 = 0.70), and karate-specific aerobic test endurance was significantly reduced ( P <.001). Conclusion: Partial sleep restriction substantially impairs both cognitive and physical performance in elite karate athletes, with compounding effects during exercise. Practically, these findings suggest that coaches should educate athletes about the importance of sleep and avoid scheduling intensive training sessions after suspected poor sleep nights. Athletes should prioritize 7 to 9 hours of consistent sleep, particularly before competitions, and minimize late-night activities that disrupt their sleep schedules. Simple sleep hygiene practices, such as maintaining regular bedtimes and avoiding screens before sleep, may help preserve performance capacity.