Journal of Applied Physiology, Vol 64, Issue 2 550-555, Copyright © 1988 by American Physiological Society
Effect of ambient temperature on protein breakdown during prolonged exercise
D. G. Dolny and P. W. Lemon
Applied Physiology Research Laboratory, Kent State University, Ohio 44240.
Male subjects (n = 8) cycled for 90 min in 5, 20, and 30 degrees C
environments. Rectal (Tre), chest, and thigh temperatures, O2 consumption
(VO2), respiratory exchange ratio (R), and venous concentrations of
glucose, free fatty acids (FFA), urea N, lactic acid (LA), norepinephrine
(NE), epinephrine (E), and cortisol (C) were measured before, during, and
after exercise. Urea N excretion was measured in 72 h of nonexercise, in 72
h of exercise (exercise day + 2 post-exercise days) urine samples, and in
exercise sweat. Calculated 72-h protein utilization (means +/- SE) was
significantly greater (P less than 0.05) for the 5 (86.9 +/- 27.1 g) and 20
(82.9 +/- 22.7 g) compared with 30 degrees C (34.01 +/- 19.1 g) trial.
Regardless of ambient temperature exercise increased the venous
concentration of C, E, and NE. These catabolic hormones were greatest in 5,
lowest in 20, and intermediate in 30 degrees C. Exercise Tre and VO2 were
greatest in the 30 degrees C environment. Venous FFA concentration was
significantly higher and R significantly lower in 5 vs. 20 or 30 degrees C,
and venous LA concentration was significantly greater in 30 vs. 20 or 5
degrees C. Although these results indicate that exercise protein breakdown
is affected by ambient temperatures, the mechanism of action is not due
solely to circulating NE, E, and C. Differences in venous FFA and LA across
environmental temperatures suggest that alterations in carbohydrate and fat
metabolism may have contributed to the observed variable protein
utilization.
