The aim of the present study was to examine the effect of a nap opportunity during the daytime realized at different times of day on physical and mental performance. Eighteen physically active males (age: 20.5 ± 3.0 years, height: 175.3 ± 5.9 cm, body-mass: 70.0 ± 8.6 kg) were tested under four experimental conditions: no-nap condition, nap at 13h00, nap at 14h00 and nap at 15h00. All nap durations were of 25-min and all tests were performed at 17h00. They performed a 5-m shuttle run test, which generated measures of the highest distance (HD) and total distance (TD). The rating of perceived exertion (RPE) was recorded after each of the six sprints in the 5-m shuttle run test. Vigilance was measured using a digit cancellation test. The results showed that TD at 17h00 was 4% greater after a nap at 14h00 than in the no-nap condition (+28 m, p < .05) or after the nap at 13h00 (+29 m, p < .05). HD was 8% higher (+9 m, p < .001) after a nap at 14h00 than in the no-nap condition and 7% higher after nap at 15h00 than in the no-nap condition (+7 m, p < .05). In addition, HD was 6% higher after nap at 14h00 (+7 m, p < .01) and 5% higher after nap at 15h00 (+9 m, p < .01) than HD after a nap at 13h00. Napping at 13h00 had no effect on physical performance at 17h00. No significant differences were observed between RPE and vigilance scores in the nap and no-nap conditions. In conclusion, napping for 25 min at 14h00 and 15h00 produces meaningful improvements in responses during repeated short-term maximal exercise tests performed at 17h00. Napping at 13h00 does not. Vigilance, as measured using a digit cancellation test, and RPE scores are not influenced by any of the nap opportunities.
Keywords: Sport; exercise performance; nap; sleep; time-of-day.