Acute caffeine intake before and after fatiguing exercise improves target shooting engagement time

INTRODUCTION: Previous research has identified acute caffeine ingestion as an effective aid in counteracting the decline in vigilance experienced during sentry duty and sustained operations. However, further research is needed to clarify caffeine's effects under various stressors and additional operational conditions. The purpose of the present study was to examine the effect of caffeine on target detection and rifle marksmanship during simulated combat operations. METHODS: There were 12 reservists who ingested 5 mg x kg(-1) body mass of caffeine (C) or placebo (P) 1 h before beginning a 2.5-h loaded march and 1.0-h sandbag wall construction task. Following exercise, participants were given a re-dose of 2.5 mg x kg(-1) body mass of C or P. An hour after ingestion, participants commenced a 2.5-h shooting session on a small arms simulator, which included friend-foe discrimination (FF) and vigilance (VIG) tasks. Marksmanship performance measures included engagement time (ET), the number of shots fired (NS), accuracy, and precision. RESULTS: C ingestion (initial and/or redose) did not affect shooting performance during the FF task. ET and NS improved during the VIG task with C ingestion (mean +/- SD of 2.82 +/- 0.27 s and 29.2 +/- 1.9 shots out of 30 targets, respectively) compared with the P trial (3.00 +/- 0.26 s and 28.0 +/- 3.0 shots; p < 0.05). CONCLUSION: Caffeine ingestion improves target detection and engagement speed during vigilance situations, but is not effective during more complex operations requiring higher levels of cognitive processing and fine motor control and coordination.