EFFECTS OF AMBIENT-TEMPERATURE ON THE CAPACITY TO PERFORM PROLONGED CYCLE EXERCISE IN MAN

Eight healthy males performed four rides to exhaustion at approximatel y 70% of their V over dot O-2max obtained in a neutral environment. Su bjects cycled at ambient temperatures (T-a) of 3.6 +/- 0.3 (SD), 10.5 +/- 0.5, 20.6 +/- 0.2, and 30.5 +/- 0.2 degrees C with a relative humi dity of 70 +/- 2% and an air velocity of approximately 0.7 m.s(-1). We ighted mean skin temperature ((T) over bar(sk)), rectal temperature (T -re), and heart rate (HR) were recorded at rest, during exercise and a t exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of hemoglobin, hematocrit, blood meta bolites, and serum electrolytes and osmolality. Expired air was collec ted for calculation of V over dot O-2 and R which were used to estimat e rates of fuel oxidation. Ratings of perceived exertion (RPE) were al so obtained. Time to exhaustion was significantly influenced by T-a (P = 0.001): exercise duration was shortest at 30.5 degrees C (51.6 +/- 3.7 min) and longest at 10.5 degrees C (93.5 +/- 6.2 min). Significant effects of T-a were also observed on V over dot (E), V over dot O-2, R, estimated fuel oxidation, HR, T-re, (T) over bar(sk), sweat rate, a nd RPE. This study demonstrates that there is a clear effect of temper ature on exercise capacity which appears to follow an inverted U relat ionship.