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Excerpt
Caffeine (CAF) has been shown to hasten self-paced work and improve cognitive function in both rested and sleep deprived individuals. As such, it represents an effective strategy for the military to counter the impairments in physical and cognitive function that occur during periods of sustained operations. PURPOSE: It was the purpose of this study to examine the effects of CAF on a 2-hour forced march followed by a subsequent sandbag piling task during the early evening and morning of a night of sleep loss. METHODS: Seventeen soldiers (26.9 ± 7.6 y, 83.3 ± 10.9 kg) performed a doubleblind CAF and placebo (PLAC) trial where each trial involved a control day and control sleep period followed by 30 hours of sustained wakefulness beginning on the second morning. A 400 mg dose of CAF was administered as a gum at 2130 h. At 2200 h, subjects began a 2-hour forced march at 6 km/h with a 2% grade with ambient conditions between 20–22°C. At midnight, subjects performed a sandbag piling task that involved moving 20 15-kg sandbags a distance of 6.5 m to construct a wall as fast as possible. This task involved 2 sets of completing 6 walls with a 5-min rest between sets. RESULTS: CAF had no effect on the heart rate (113.7 ± 10.4 vs 112.5 ± 10.2 b/min for PLAC and CAF, respectively), rating of perceived exertion (11.1 ± 2.1 vs 10.7 ± 2.6 for PLAC and CAF, respectively) or VO2 (1.51 ± 0.20 vs 1.55 ± 0.20 l/min for PLAC and ACF, respectively) throughout the forced march. Time to complete the 6 walls during set 1 was significantly reduced with CAF (13.0 ± 1.1 min) vs PLAC (13.8 ± 1.1 min) but there was no difference during set 2 for CAF (13.5 ± 1.6 min) or PLAC (13.6 ± 1.2 min). CONCLUSIONS: It was concluded that CAF did not influence the physiological and perceptual strain during a forced march but CAF was effective in improving performance during the early phase of a self-paced sandbag piling task.
