Abstract

While there are many factors that could lead to muscle fatigue during exercise in the heat, the interaction between metabolic and thermoregulatory factors has not been examined extensively. PURPOSE: To examine the effects of environment (hot = 38oC and cold =10oC) and intensity (80 & 100% VO2max), on cycling time-to-exhaustion (TTE), pH, LA, core temperature (Tc), and related metabolic variables. METHODS: Ten subjects completed four TTE trials: 1) Hot, 80% VO2max (H80), 2) Cold 80% (C80), 3) Hot 100% (H100), and 4) Cold 100% (C100). Subjects were fitted with an esophageal probe for Tc, a heart rate (HR) monitor, and a catheter in a forearm vein for blood sampling prior to a 5-min warm-up completed at 23o C. Blood was taken at rest, every 5 min during exercise, at exhaustion, and 3 min post-exercise and analyzed for pH, HCO3 -, and K+. VO2 and HR data were measured continuously. Lactate (LA) was measured using a spectrophotometric, enzymatic assay. Repeated measures ANOVA (Condition x Intensity x Time) was used to determine differences. RESULTS: All values are at exhaustion.TableCONCLUSIONS:During the longer, less intense trials (H80 & C80), Tc was higher; thus, it likely played a greater role in muscular fatigue, while during the shorter, more intense trials (H100 & C100), pH may have been a more important factor.

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