Ganio, M. S., Klau, J. F., Johnson, E. C., Casa, D. J., Volek, J. S., Anderson, J. M., Mares, C. M., & Armstrong, L. E. (2009). Effect of ambient temperature on caffeine ergogenicity during endurance exercise. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 877.

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"It is well-established that caffeine ingestion during exercise enhances aerobic performance. Conversely, the physiological and psychological strain that accompanies increased ambient temperature may result in decreased aerobic performance. Little is known about the interaction of environmental temperature and caffeine effects on aerobic cycling performance."

This study compared the effects of ambient temperature (12C and 33C) on caffeine ergogenicity during endurance cycling exercise. Male cyclists (N = 11) completed four exercise trials. After cycling continuously for 90 minutes (15-minutes alternating intensities of ~60 and ~71% VO2max) in either a warm (~33C, ~41% RH) or cool (~12C, ~60% RH) environment, Ss completed a 15-minute performance trial. Ss ingested 3 mg/kg of caffeine or placebo in capsules 60 minutes prior to exercise and after 45 minutes of exercise. Prior to, and at every 15 minutes of exercise, Ss ingested water in equal volumes so that independent of ambient temperature were dehydrated less than 1% at the end of exercise (i.e., greater fluid was ingested in the 33C condition compared to the 12C condition).

Total work accumulated during the performance trial was greater in 12C than 33C. Independent of temperature, caffeine increased performance time when compared to placebo. However, compared to placebo, caffeine increased performance time in the 12C but not in the 33C condition. Within the 12C trial, significant differences between caffeine and placebo occurred from 0-5 minutes and 5-10 minutes, but not 10-15 minutes.

Implication. The ergogenic effects of caffeine are reduced as temperature increases. As well, in accommodating temperatures, caffeine's most notable effects occur early in aerobic performance.

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