Effects of a hot environment on simulated cycling and running performance in triathletes

Aim. This study examined the effects of a hot environment on metabolic responses, thermoregulation, and performance during simulated cycling and running in triathletes. Methods. Seven male triathletes completed two trials in moderate (22±0.2 °C, 76±2% relative humidity, M) and hot (31.2±0.2 °C, 76.4±1.6% relative humidity, H) environmental conditions separated by at least 7 days. The subjects were required to complete a self-paced 40 km simulated cycling, followed by a 10 km run on a treadmill for as fast as possible in both trials. Results. The overall performance time was faster in M than H (M vs H, 119±6 min vs 127±6 min, P<0.01). Moreover, there were no differences in the cycling time between the two trials, but the run time was faster in M (M vs H, 51±4 min vs 59±5 min, Plt;0.05) than in H. Ad libitum water consumption was higher in H than in M (H vs M, 970±231 mL◇min^-1 vs 547±131 mL◇min ^-1 Plt;0.05), and the mean skin temperature was also higher in H than in M throughout the exercise (H vs M, 35.3±0.1 vs 33.3±0.1 °C, Plt;0.05). However, there were no differences in rectal temperature, blood lactate, blood glucose, body mass change, plasma volume change, osmolality, carbohydrate oxidation, and fat oxidation between the trials. Conclusion. The results suggested that triathletes reduced their running performance after a 40 km simulated cycling when the ambient temperature was high.