The effects of caffeine on the diurnal variation of the reaction time and short-term maximal performance after one night of sleep deprivation

The present study aimed to investigate the effects of caffeine ingestion and one night of total sleep deprivation on the diurnal variation of cognitive and short-term maximal performances. In a randomized order, thirteen active male completed eight test sessions at 08:00 h and 18:00 h after a placebo or caffeine ingestion (5 mg•kg-1) after a reference night (RN) or a night of total sleep deprivation (TDN). During each session participants performed the simple and the choice reaction time (SRT and CRT), the profile of mood states (POMS), the squat jump (SJ) and the 30-s Wingate tests (peak (PP) and mean (MP) powers and the fatigue index (FI)).After RN, PP, MP and SJ improved significantly from the morning to the afternoon (P<0.001). In the placebo condition compared to RN, they decreased significantly after TSD only in the afternoon (p<0.001). However, POMS, SRT and CRT increased significantly after TSD (p<0.001).The caffeine ingestion improved PP, SRT, CRT and POMS after TSD compared to RN (p<0.001) and SJ after the two sleep conditions (p<0.001). Therefore, POMS, SRT, CRT and physical performances are time-of-day dependent and caffeine is an effective strategy to counteract the effect of sleep loss on these performances.