The effect of air temperature on physical working capacity.

Measurements were taken in ten healthy young male subjects, ages 20 to 25, under air temperature conditions of 5, 20, 35, and 50 degrees C. The relative humidity was maintained at 50% throughout all the air temperature conditions. Maximum work loads were obtained by treadmills. The first work load was 95 m/min 0 degrees grade; this was increased by 1 degree every one minute until the subjects reached a self-imposed maximum. The heart rate and expired air sample during the last 30 sec work was used for statistical analyses. The analysis of variance confirmed a significance effect of air temperature factor in the cases of the endurance time until the exhaustion, maximal oxygen uptake, maximal carbon dioxide production, heart rate, respiratory exchange ratio, and oxygen pulse. The regression analyses disclosed the following relationships between maximal oxygen uptake (VO2 max) or heart rate (HR) and air temperature: VO2 max = 2472 + 29.5Ta-0.6Ta2(ml. STPD), HR = 173 + 2.0Ta-0.09Ta2 + 0.001Ta3, where Ta shows air temperature in centigrade. The physiological mechanism underlying the changes in maximal oxygen uptake in heat is discussed.