Muscle metabolism during exercise and heat stress in trained men: effect of acclimation.
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 degrees C and 20% relative humidity (RTT) or 40 degrees 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.
Febbraio
M A
MA
Exercise Metabolism Unit, Victoria University of Technology, Footscray, Australia.
Snow
R J
RJ
Hargreaves
M
M
Stathis
C G
CG
Martin
I K
IK
Carey
M F
MF
D000064:Acclimatization; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001831:Body Temperature; D002395:Catecholamines / Q000097:blood; D015444:Exercise; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D007773:Lactates / Q000097:blood / Q000378:metabolism; D019344:Lactic Acid; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010806:Physical Education and Training; D005082:Physical Exertion; D013312:Stress, Physiological / Q000378:metabolism*
D001786:Blood Glucose; D002395:Catecholamines; D007773:Lactates; D019344:Lactic Acid