Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion

Douglas G. Bell, Ira Jacobs, Tom M. McLellan, Masami Miyazaki, Catht M. Sabtstdm

Research output: Contribution to journalArticle

18 Citations (Scopus)

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% V̇O2peak in a 40°C and 30% RH environment until rectal temperature reached 39.3°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 Faro 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 (T̄sk), rectal temperature (Tre), V̇O2, V̇CO2, V̇E, 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 T̄sk, initial Tre, Δ Tre, SR or the sensation of thermal comfort. V̇O2 and V̇E, 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.

Original languageEnglish
Pages (from-to)583-588
Number of pages6
JournalAviation Space and Environmental Medicine
Volume70
Issue number6
Publication statusPublished - 1999 Jun 1
Externally publishedYes

Fingerprint

Eating
Hot Temperature
Temperature
Sweat
Heart Rate
Placebos
Body Temperature
Ephedrine
Skin Temperature
Thermogenesis
Body Temperature Regulation
Dizziness
Caffeine
Nausea
Therapeutics
ephedrine drug combination caffeine

Keywords

  • Ergogenic
  • Heat stress
  • Metabolism
  • Methylxanthine
  • Sympathomimetic

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health

Cite this

Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion. / Bell, Douglas G.; Jacobs, Ira; McLellan, Tom M.; Miyazaki, Masami; Sabtstdm, Catht M.

In: Aviation Space and Environmental Medicine, Vol. 70, No. 6, 01.06.1999, p. 583-588.

Research output: Contribution to journalArticle

Bell, Douglas G. ; Jacobs, Ira ; McLellan, Tom M. ; Miyazaki, Masami ; Sabtstdm, Catht M. / Thermal regulation in the heat during exercise after caffeine and ephedrine ingestion. In: Aviation Space and Environmental Medicine. 1999 ; Vol. 70, No. 6. pp. 583-588.
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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{\%} V̇O2peak in a 40°C and 30{\%} RH environment until rectal temperature reached 39.3°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 Faro 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 (T̄sk), rectal temperature (Tre), V̇O2, V̇CO2, V̇E, 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 T̄sk, initial Tre, Δ Tre, SR or the sensation of thermal comfort. V̇O2 and V̇E, 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.",
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