The effect of drinking ad-libitum on performance during a 40-km cycling time trial in the heat

Purpose The main purpose of this study was to investigate if drinking ad-libitum can counteract potential negative effects of a hypohydrated start during a 40-km time trial in the heat. Methods Twelve well-trained males performed one 40-km cycling time trial while starting euhydrated (EU: no water during the time trial) and two 40-km cycling time trials while starting hypohydrated. During one hypohydrated trial no fluid was ingested (HYPO), during the other trial ad-libitum water ingestion was allowed (FLUID). Ambient temperature was 35.2 ± 0.2°C, relative humidity was 51 ± 3% and airflow 7 m·s-1. Body mass was determined at the start of the test, and before and after the time trial. During the time trial, power output, heart rate, gastrointestinal temperature, mean skin temperature, RPE, thermal comfort, thermal sensation and thirst sensation were measured. Results Prior to the start of the time trial, body mass was 1.2% lower in HYPO and FLUID compared to EU. During the time trial, body mass loss in FLUID was lower compared to EU and HYPO (1.0 ± 0.8%, 2.7 ± 0.2% and 2.6 ± 0.3%, respectively). Hydration status had no effect on power output, heart rate, RPE, gastrointestinal and mean skin temperature, thermal sensation and thermal comfort. Thirst sensation was higher in HYPO than in the other two conditions. Conclusion Hypohydration did not adversely affect exercise performance during a 40-km cycling time trial in the heat. Therefore, whether or not participants consumed fluid during exercise could not influence their time trial performance.