The combined effect of heat stress and hypohydration on pacing pattern during a 40 - km cycling time trial

Purpose To determine the combined effect of hypohydration and heat stress on pacing pattern and performance during a 40-km cycling time trial. Methods 13 Male cyclists performed 40-km cycling time trials in 25.3 ± 0.3°C and 35.3 ± 0.2°C in a euhydrated (EU25, EU35), and hypohydrated (HYPO25, HYPO35) state. Relative humidity was 55 ± 3% and air velocity was 7 m·s-1. Hypohydration was induced before starting the time trial by 50 min exercise in 30.2 ± 0.2°C and 55 ± 1% relative humidity. Results Body mass at the start of the time trial was 1.2% lower in the HYPO trials than in the EU trials. At the finish, hydration levels were-2.1 ± 0.4% (EU25),-2.7 ± 0.3% (EU35),-3.1 ± 0.3% (HYPO25), and-3.8 ± 0.4% (HYPO35) of initial body mass. Heat stress increased finish time whereas a trend was observed for hypohydration. No interaction effect between heat stress and hydration status on finish time was found. Heat storage, skin temperature, thermal sensation/comfort and RPE were higher in the hot trials, whereas RPE and thirst sensation were higher in the hypohydration trials. Conclusion The negative effect of hypohydration on exercise performance during a 40-km cycling time trial is similar in hot and moderate conditions, probably because of the provided wind cooling.