Caffeine improves physical performance during 24 h of active wakefulness.

Reductions in both cognitive and physical performance occur during periods of sleep loss with sustained operations. It was the purpose of this study to examine the effects of caffeine on activities chosen to simulate the physical challenges that might occur during a military scenario involving a period of sleep loss.There were 16 subjects (26.7 +/- 7.8 yr, 83.8 +/- 11.0 kg) who completed a double-blind caffeine and placebo trial involving a control day and sleep period followed by 28 h of sleep deprivation. A 400-mg dose of caffeine was administered at 21:30 followed by subsequent 100-mg doses at 03:00 and 05:00. At 22:00, subjects began a 2-h forced march followed by a sandbag piling task. A treadmill run to exhaustion at 85% of maximal aerobic power was performed at 07:00 of the second day of sleep deprivation.Caffeine had no effect on the heart rate or oxygen consumption, but rating of perceived exertion (RPE) was reduced with caffeine during the forced march. Time to complete the sandbag piling task during set 1 was significantly reduced with caffeine (12.9 +/- 1.0 min) compared with placebo (13.8 +/- 1.0 min) but there was no difference during set 2 and RPE was increased. Time to exhaustion was significantly increased 25% during the run with caffeine (17.0 +/- 4.4 min) compared with placebo (13.5 +/- 3.3 min), and caffeine maintained performance at control levels (16.9 +/- 4.6 min).It was concluded that caffeine is an effective strategy to maintain physical performance during an overnight period of sleep loss at levels comparable to the rested state.