The Effectof Caffeineon Run Timesto Exhaustionat 85% VO2max Followinga Nightof Sleep Loss

Abstract

0141 Caffeine (CAF) has been shown to extend exercise times to exhaustion 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 run times to exhaustion (TE) at 85% VO2max following a 24-hour period of wakefulness. METHODS: Eighteen soldiers (26.4 ± 7.4 y, 85.0 ± 11.0 kg) performed a double-blind 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 followed by subsequent 100 mg doses at 0300 and 0500 h. Following the assessment of other physical tasks, cognitive function and marksmanship, subjects performed a treadmill run to exhaustion at 0700 hours of the third morning. RESULTS: CAF had no effect on heart rate (176.2 ± 6.3 vs 175.0 ± 7.1 b/min for CAF and PLAC, respectively), ratings of perceived exertion (14.8 ± 2.3 vs 14.9 ± 2.5 for CAF and PLAC, respectively) or VO2 (3.30 ± 0.43 vs 3.30 ± 0.39 l/min for CAF and PLAC, respectively) after 10 minutes of exercise. TE was significantly increased by 24% with CAF (16.3 ± 4.6 min) compared with PLAC (13.2 ± 3.2 min) and CAF maintained performance at control levels (16.2 ± 4.8 min). CAF had a similar effect on TE for users (> 300 mg/day, n = 5) (15.9 ± 5.5 vs 12.8 ± 3.7 min for CAF and PLAC, respectively) compared with non-users (< 10 mg/day, n = 5) (16.9 ± 3.7 vs 14.9 ± 1.9 min for CAF and PLAC, respectively). CONCLUSIONS: It was concluded that the use of repeated doses of CAF during a 24-hour period of sustained wakefulness is an effective strategy to maintain physical performance at levels comparable to the rested state.