Muscle metabolism during exercise and heat stress in trained men: Effect of acclimation

M. A. Febbraio, R. J. Snow, M. Hargreaves, C. G. Stathis, I. K. Martin, M. F. Carey

Research output: Contribution to journalArticleResearchpeer-review

168 Citations (Scopus)


Exercise metabolism was examined in 13 endurance athletes who exercised on three occasions for 40 min at 70% of maximal O2 uptake in an environmental chamber at either 20°C and 20% relative humidity (RTT) or 40°C and 20% relative humidity before (PRE ACC) or after (POST ACC) 7 days of acclimation. Exercise in the heat resulted in a lower (P < 0.05) mean O2 uptake (0.13 l/min) and higher (P < 0.01) heart rate and respiratory exchange ratio. Acclimation resulted in a lower (P < 0.01) mean heart rate and respiratory exchange ratio. Postexercise rectal temperature, muscle temperature, muscle and blood lactate, and blood glucose were higher (P < 0.01) in the PRE ACC than in the RTT trial, but all were reduced (P < 0.01) in the POST ACC compared with the PRE ACC trial. Muscle glycogenolysis and percentage of type I muscle fibers showing glycogen depletion were greater (P < 0.05) in the PRE ACC than in the RTT trial. Muscle glycogenolysis was unaffected by acclimation during exercise in the heat, although the percentage of depleted type I fibers was higher (P < 0.05) in the unacclimated state. Plasma epinephrine was higher (P < 0.01) during exercise in the heat in the unacclimated individual relative to RTT but was lower (P < 0.01) in the POST ACC than in the PRE ACC trial. The greater reliance on carbohydrate as a fuel source during exercise in the heat appears to be partially reduced after acclimation. These alterations are consistent with the observed changes in plasma epinephrine concentrations.

Original languageEnglish
Pages (from-to)589-597
Number of pages9
JournalJournal of Applied Physiology
Issue number2
Publication statusPublished - 1 Jan 1994
Externally publishedYes


  • catecholamines
  • environmental stress
  • fiber types
  • glycolysis
  • muscle temperature

Cite this