In a study, caffeine improved cycling performance time in a surrounding temperature of 12°C but not in a 33°C temperature. The effects of ambient temperature (12°C and 33°C) on how caffeine affects performance during endurance cycling exercise were examined. Male cyclists (N = 11) completed four exercise trials. After cycling continuously for 90 minutes (15-minutes alternating intensities of ~60 and ~71% max oxygen consumption [VO2max]) in either a warm (~33°C, ~41% RH) or cool (~12°C, ~60% RH) environment, participants completed a 15-minute performance trial. Participants 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, individuals drank water in equal volumes so that independent of ambient temperature were dehydrated less than 1% at the end of exercise (there was greater fluid intake in the 33°C condition compared to the 12°C condition). Total work accumulated during the performance trial was greater in 12°C than 33°C. Independent of temperature, caffeine increased performance time when compared to placebo. However, compared to placebo, caffeine increased performance time in the 12°C but not in the 33°C condition. Within the 12°C trial, significant differences between caffeine and placebo occurred from 0-5 minutes and 5-10 minutes, but not 10-15 minutes. (9)
