Caffeine maintains vigilance and marksmanship in simulated urban operations with sleep deprivation.

The purpose of this study was to examine the effects of caffeine (CAF) on physical, vigilance, and marksmanship tasks in soldiers during a sustained 55-h field exercise.There were 30 soldiers (23.6 +/- 4.5 yr, 81.8 +/- 10.3 kg) who were divided into a placebo (PLAC) and a CAF group. After a period of restricted sleep of 3 h during the first night, a period of sustained wakefulness began that ended at 11:00 of the third day. PLAC or CAF doses of 100 mg, 200 mg, 100 mg, and 200 mg were administered at 21:45, 23:45, 01:45, and 03:45, respectively. At 22:00 of day 2, subjects began two cycles of marksmanship, urban operations vigilance, and psychomotor vigilance (PVT) testing which ended at 06:00 of day 3.CAF maintained marksmanship vigilance at 85% throughout the second night as compared with PLAC, who significantly declined to 61.4 +/- 28.2% overnight. Marksmanship accuracy also decreased significantly in PLAC from 95.1 +/- 8.3% to 83.3 +/- 19.2%, but no change was observed in CAF. Urban operations vigilance decreased for both groups over the night, but the decrease was less for CAF (81.2 +/- 14.4% to 63.4 +/- 24.1%) compared with PLAC (77.6 +/- 19.2% to 44.0 +/- 30.2%). Reaction time and the number of major and minor lapses with the PVT significantly increased in PLAC but were unaffected in CAF.It was concluded that CAF was an effective strategy to sustain vigilance and psychomotor performance during military operations involving sleep deprivation.