Influence of Environmental Temperature on 40 km Cycling Time-Trial Performance

The purpose of this study was to examine the effect of environmental temperature on variability in power output, self-selected pacing strategies, and performance during a prolonged cycling time trial. Nine trained male cyclists randomly completed four 40 km cycling time trials in an environmental chamber at 17 degrees C, 22 degrees C, 27 degrees C, and 32 degrees C (40% RH). During the time trials, heart rate, core body temperature, and power output were recorded. The variability in power output was assessed with the use of exposure variation analysis. Mean 40 km power output was significantly lower during 32 degrees C (309 +/- 35 W) compared with 17 degrees C (329 +/- 31 W), 22 degrees C (324 +/- 34 W), and 27 degrees C (322 +/- 32 W). In addition, greater variability in power production was observed at 32 degrees C compared with 17 degrees C, as evidenced by a lower (P = .03) standard deviation of the exposure variation matrix (2.9 +/- 0.5 vs 3.5 +/- 0.4 units, respectively). Core temperature was greater (P < .05) at 32 degrees C compared with 17 degrees C and 22 degrees C from 30 to 40 km, and the rate of rise in core temperature throughout the 40 km time trial was greater (P < .05) at 32 degrees C (0.06 +/- 0.04 C.km(-1)) compared with 17 degrees C (0.05 +/- 0.05 degrees C.km(-1)). This study showed th at time-trial performance is reduced under hot environmental conditions, and is associated with a shift in the composition of power output. These finding provide insight into the control of pacing strategies during exercise in the heat.