Thermal Regulation in the Heat During Exercise After Caffeine and Ephedrine Ingestion


  1. Bell, D.G.
  2. Jacobs, I.
  3. McLellan, T.M.
  4. Miyazaki, M.
  5. Sabiston, C.M.
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
Ingesting a combination of caffeine and ephedrine (C+E) has been shown to raise metabolic heat production and body temperature. This side effect of C+E ingestion may be positive during a cold stress scenario, however, during heat stress it could prove to be detrimental. Thus, the purpose of this study was to clarify the effect of C+E ingestion on body temperature regulation during moderate exercise in a hot dry environment. Ten, healthy, non heat acclimated, males exercised at 50% V02peak in a 40C and 30% RH environment until rectal temperature reached 39.3C; heart rate (HR) remained at 95% of peak value or greater for 3 min, dizziness or nausea precluded further exercise, or 3 h had elapsed. They did this four times at weekly intervals: familiarization (Fam), control (Cont), placebo, and C+E (5 mg-kg1(-) caffeinge + 1 mg-kg(-) ephedrine) trials. The Fam and Cont treatments were done first and sequentially while the placebo and C+E treatnebts were balanced and double-blind. Tolerance times, mean skin temperature (Tsk), rectal temperature (Tre), Vo2, Vco2, VE, sweat rate (SR), HR, and sensation of thermal confort were measured. Tolerance times (mean + or - SD in minutes) were similar for the placebo (120.0 + or - 28.4) and C+E (121.3 + or - 33.9) trials and both times were significantly longer than Cont (106.6 + or - 24.0) trial. C+E did not affect Tsk, initial Tre, increment Tre, SR or the sensation of thermal conform.
Ergogenic aids;Physical training;Human performance;Methylxanthine;Sympathomimetic
Report Number
DCIEM-98-P-39 — Reprint
Date of publication
01 Mar 1998
Number of Pages
Reprinted from
Aviation, Space, and Environmental Medicine, Vol 70, no 6, 1999, p 583-588
Hardcopy;Document Image stored on Optical Disk

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