Caffeine Effects on Physical and Cognitive Performance During Sustained Operations

McLellan TM, Kamimori GH, Voss DM, Tate C, Smith SJR. Caffeine effects on physical and cognitive performance during sustained operations. Aviat Space Environ Med 2007; 78:871–877.



Purpose: This study examined caffeine (CAF) effects on physical performance and vigilance during 4 d and 3 nights of sustained operations in Special Forces personnel. Methods: There were 20 soldiers (28.6 ± 4.7 yr, 177.6 ± 7.5 cm, 81.2 ± 8.0 kg) who were divided equally into placebo (PLAC) and CAF groups. A 4-km run that included three obstacles (OBST) was completed each morning with the performance on Day 2 representing control (CON) after familiarization on Day 1 and an 8-h sleep. From 01:30 to 06:15 of Days 3–5, soldiers performed two 2-h vigilance (VIG) sessions in the field. PLAC or 200 mg of CAF was administered at 21:45 of Days 2–4 and at 01:00, 03:45, and approximately 07:00 on Days 3–5. The run commenced within 30 min of the final dose. Soldiers were provided a 4-h sleep period from 13:30–17:30 during Days 3 and 4. Results: VIG during Days 3–5 was greater for CAF vs. PLAC and not different from CON. Total run time was faster for CAF (29.7 ± 2.0 min) compared with PLAC (30.7 ± 2.9 min) on Day 3 due to faster completion of OBST (8.7 ± 0.7 min vs. 9.2 ± 1.0 min for CAF and PLAC, respectively). Thereafter, run times decreased for both groups on Days 4 and 5 compared with CON due primarily to an increased pace between OBST. Conclusions: It was concluded that CAF maintained both vigilance and physical performance during sustained operations that require periods of overnight wakefulness and restricted opportunities for daytime sleep.