Bell, D. G., & McLellan, T. M. (2003). Repeated exercise performance and caffeine ingestion. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 1476.

Male caffeine users (N = 9) performed exercise rides at 80% VO2max to exhaustion after ingesting a placebo, 5 mg/kg caffeine, and 2.5 mg/kg caffeine one hour before exercise. Two rides were performed weekly on the same day, one in the morning and five hours later in the afternoon. There were four treatments mixing the two levels of caffeine and placebo.

• Condition A - 5 mg/kg caffeine in the AM, and 2.5 mg/kg caffeine in the PM.
• Condition B - placebo in the AM, and placebo in the PM.
• Condition C - 5 mg/kg caffeine in the AM, and placebo in the PM.
• Condition D - placebo in the AM, and 5 mg/kg caffeine in the PM.

Caffeine ingestion significantly improved time to exhaustion in the AM. Caffeine also provided a significant effect in the PM regardless of whether caffeine or placebo was ingested in the AM. AM caffeine ingestion maintained its effect in PM placebo conditions.

Implication. Caffeine ingestion in the morning provided AM and PM aerobic performance enhancements.

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