Partial sleep restriction (4 hours) substantially impairs both cognitive and physical performance in elite karate athletes, with compounding effects during exercise.
Key Findings
Results
Sleep restriction significantly increased Stroop reaction times in elite karate athletes, with further deterioration following exercise.
Stroop reaction times increased under sleep restriction (F = 13.0, P < .01, ηp2 = 0.50)
Further deterioration was observed post-exercise (F = 60.27, P < .001, ηp2 = 0.90)
The large effect size post-exercise (ηp2 = 0.90) indicates a very strong relationship between sleep restriction and Stroop performance after physical exertion
Study used a randomized crossover design with 14 international-level male karate athletes comparing 8-hour regular sleep vs. 4-hour sleep restriction conditions
Results
Simple reaction time declined significantly following sleep restriction.
Simple reaction time showed significant decline under sleep restriction (F = 27.2, P < .001, ηp2 = 0.70)
The effect size of ηp2 = 0.70 indicates a large effect of sleep restriction on simple reaction time
Participants were 14 international-level male karate athletes with a mean age of 23.35 ± 4.61 years
The two experimental sessions were separated by 1 week to allow for washout
Results
Multiple-choice reaction time was unaffected by sleep restriction at rest but worsened significantly after exercise.
Multiple-choice reaction time remained unaffected at rest under sleep restriction conditions
After exercise, multiple-choice reaction time worsened significantly (F = 5.3, P < .05, ηp2 = 0.30)
The moderate effect size (ηp2 = 0.30) suggests a meaningful but smaller impact compared to other cognitive measures
This pattern suggests that physical exertion may unmask cognitive deficits that are not apparent at rest under sleep restriction
Results
Squat jump height decreased significantly under sleep restriction conditions.
Squat jump height decreased under sleep restriction (F = 15.8, P < .001, ηp2 = 0.50)
The effect size of ηp2 = 0.50 indicates a large effect of sleep restriction on explosive lower-body power
Physical performance was evaluated both before and after exercise in both experimental conditions
This finding indicates that neuromuscular performance relevant to karate (explosive power) is compromised by reduced sleep
Results
Agility performance as measured by the modified agility T-test deteriorated significantly under sleep restriction.
Modified agility T-test (MAT) performance deteriorated under sleep restriction (F = 28.5, P < .001, ηp2 = 0.70)
The large effect size (ηp2 = 0.70) indicates a strong relationship between sleep restriction and agility performance
The MAT is a sport-relevant physical performance test assessing multi-directional movement speed
This result is particularly relevant for karate, where rapid directional changes are fundamental to performance
Results
Karate-specific aerobic endurance was significantly reduced following sleep restriction.
Karate-specific aerobic test endurance was significantly reduced under sleep restriction (P < .001)
A karate-specific aerobic test was used to assess sport-relevant endurance capacity
All physical tests were conducted both before and after exercise in each experimental session
This finding suggests that aerobic capacity relevant to sustained competitive karate performance is impaired by insufficient sleep
Methods
The study design involved 14 elite male karate athletes completing two randomized sessions under regular sleep and sleep restriction conditions.
Participants were 14 international-level male karate athletes with mean age 23.35 ± 4.61 years
A randomized crossover design was used with two experimental sessions separated by 1 week
Regular sleep was defined as 8 hours and sleep restriction as 4 hours
Cognitive performance was assessed using the Stroop test, simple reaction time, and multiple-choice reaction time tests
Physical performance was evaluated through squat jump, modified agility T-test, and karate-specific aerobic test, all conducted before and after exercise
What This Means
This research suggests that cutting sleep in half — from 8 hours to just 4 hours — significantly harms both the mental sharpness and physical abilities of elite karate competitors. The study tested 14 international-level male karate athletes twice, once after a full night's sleep and once after only 4 hours, measuring how quickly they could react, process conflicting information, jump, change direction, and sustain aerobic effort. Nearly every measure of performance worsened when athletes were sleep-restricted, with some of the largest impairments appearing after a bout of exercise rather than at rest.
A particularly notable finding was that some cognitive effects — specifically the ability to choose between multiple responses quickly — only became apparent after physical exertion. This suggests that exercise can expose hidden sleep-deprivation deficits that might not be obvious when an athlete is simply standing still. The impairments in agility and reaction time are especially significant for karate, a sport where split-second decisions and rapid directional changes can determine the outcome of a match.
This research suggests that sleep is a critical but sometimes overlooked component of athletic preparation in combat sports. The findings point to practical implications for coaches and athletes: scheduling hard training sessions after nights of poor sleep may be counterproductive, and consistent sleep of 7 to 9 hours — especially in the days leading up to competition — may help preserve both mental and physical readiness. Simple habits like keeping regular bedtimes and limiting screen use before sleep could make a meaningful difference in performance capacity.
Amri A, Faleh J, Ben Aissa M, Ceylan H, Ben Hassen S, Hmaidi J, et al.. (2026). Effects of sleep restriction on cognitive and physical performance in elite karate athletes: A randomized crossover study.. Medicine. https://doi.org/10.1097/MD.0000000000048064