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Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion.
Aviat Space Environ Med. 1999 Jun; 70(6):583-8.AS

Abstract

BACKGROUND

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.

METHODS

Ten, healthy, non heat acclimated, males exercised at 50% VO2peak in a 40 degrees C and 30% RH environment until rectal temperature reached 39.3 degrees C; 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 . kg(-1) caffeine + 1 mg . kg(-1) ephedrine) trials. The Fam and Cont treatments were done first and sequentially while the placebo and C+E treatments 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 comfort were measured.

RESULTS

Tolerance times (mean+/-SD in minutes) were similar for the placebo (120.0+/-28.4) and C+E (121.3+/-33.9) trials and both times were significantly longer than Cont (106.6+/-24.0) trial. C+E did not affect Tsk, initial TrC, delta Tre, SR or the sensation of thermal comfort. VO2 and VF, were significantly increased by C+E. HR was elevated by C+E compared with the other trials, but only during the initial 20 min of exercise.

CONCLUSION

Although the metabolic rate was slightly increased with C+E treatment, it was sufficiently offset by increased heat loss mechanisms so that internal body temperature was not increased during moderate exercise in a hot, dry environment.

Authors+Show Affiliations

Defense and Civil Institute of Environmental Medicine, Toronto, Ontario, Canada.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Clinical Trial
Controlled Clinical Trial
Journal Article

Language

eng

PubMed ID

10373050

Citation

Bell, D G., et al. "Thermal Regulation in the Heat During Exercise After Caffeine and Ephedrine Ingestion." Aviation, Space, and Environmental Medicine, vol. 70, no. 6, 1999, pp. 583-8.
Bell DG, Jacobs I, McLellan TM, et al. Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion. Aviat Space Environ Med. 1999;70(6):583-8.
Bell, D. G., Jacobs, I., McLellan, T. M., Miyazaki, M., & Sabiston, C. M. (1999). Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion. Aviation, Space, and Environmental Medicine, 70(6), 583-8.
Bell DG, et al. Thermal Regulation in the Heat During Exercise After Caffeine and Ephedrine Ingestion. Aviat Space Environ Med. 1999;70(6):583-8. PubMed PMID: 10373050.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion. AU - Bell,D G, AU - Jacobs,I, AU - McLellan,T M, AU - Miyazaki,M, AU - Sabiston,C M, PY - 1999/6/18/pubmed PY - 1999/6/18/medline PY - 1999/6/18/entrez SP - 583 EP - 8 JF - Aviation, space, and environmental medicine JO - Aviat Space Environ Med VL - 70 IS - 6 N2 - BACKGROUND: 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. METHODS: Ten, healthy, non heat acclimated, males exercised at 50% VO2peak in a 40 degrees C and 30% RH environment until rectal temperature reached 39.3 degrees C; 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 . kg(-1) caffeine + 1 mg . kg(-1) ephedrine) trials. The Fam and Cont treatments were done first and sequentially while the placebo and C+E treatments 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 comfort were measured. RESULTS: Tolerance times (mean+/-SD in minutes) were similar for the placebo (120.0+/-28.4) and C+E (121.3+/-33.9) trials and both times were significantly longer than Cont (106.6+/-24.0) trial. C+E did not affect Tsk, initial TrC, delta Tre, SR or the sensation of thermal comfort. VO2 and VF, were significantly increased by C+E. HR was elevated by C+E compared with the other trials, but only during the initial 20 min of exercise. CONCLUSION: Although the metabolic rate was slightly increased with C+E treatment, it was sufficiently offset by increased heat loss mechanisms so that internal body temperature was not increased during moderate exercise in a hot, dry environment. SN - 0095-6562 UR - https://www.unboundmedicine.com/medline/citation/10373050/Thermal_regulation_in_the_heat_during_exercise_after_caffeine_and_ephedrine_ingestion_ L2 - https://medlineplus.gov/exerciseandphysicalfitness.html DB - PRIME DP - Unbound Medicine ER -