Perception of effort during high-intensity exercise at low, moderate and high wet bulb globe temperatures.

The purpose of this study was to determine the effect of low, moderate and high wet bulb globe temperatures (Twbg) on cardiovascular variables and ratings of perceived exertion (RPE) during moderately prolonged, high-intensity exercise. Six subjects [four men and two women; mean (SD) age, 22.0 (1.2) years; maximum oxygen consumption (VO2peak), 51.0 (8.4) ml.kg-1.min-1] completed 30 min of exercise (80% VO2peak) on a cycle ergometer at low [14.7 (2.1) degrees C], moderate [21.0 (1.5) degrees C], and high [27.4 (2.3) degrees C] Twbg. Two additional subjects completed 20 min of exercise in the high temperature condition, but completed 30 min in the moderate and low Twbg. Heart rate (fc), blood pressure, blood lactate (La), mean skin temperature (Tsk), VO2, and RPE were measured at 10, 20 and 30 min. Results showed that fc, rate pressure product, RPE, pulmonary ventilation and ventilatory equivalent for oxygen increased (P < 0.05) across time for all conditions, while P(a) decreased across time. Tsk and fc were significantly greater across time in the high condition [35.9 (0.65) degrees C; 176 (12.6) beats.min-1] compared to the moderate [34.6 (1.5) degrees C; 170 (17.2) beats.min-1] and the low condition [31.7 (1.5) degrees C; 164 (17.1) beats.min-1]. However, there were no differences throughout exercise in RPE [high, 16.2 (2.0); moderate, 16.4 (2.2); low, 16.3 (1.9)] and VO2 across the conditions. These data suggest that RPE is closely related to metabolic intensity but is not a valid indicator of cardiovascular strain during exercise in high Twbg conditions.