Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat

Using intravenous infusion, we separated the physiologic consequences of 3% body mass dehydration from the conscious awareness of fluid replacement on time trial ( TT ) performance in the heat. Eleven trained cyclists performed 90 min of steady‐state (50%V ˙ O 2 peak) cycling followed by a self‐paced 20‐km TT in a hot–dry (35 ° C , 10% relative humidity, wind speed 3.0 m/s) environment while euhydrated‐not thirsty ( EU‐NT ), euhydrated‐thirsty ( EU‐T ), dehydrated‐not thirsty ( DH‐NT ), or dehydrated‐thirsty ( DH‐T ). Thirst was manipulated by providing ( NT ) or withholding ( T ) ad libitum 35 ° C water oral rinse. Distinct hydration states existed, with 0.4 ± 0.5% dehydration following the 20‐km TT ( EU ) compared with 3.2 ± 0.6% in DH ( P  < 0.001). Greater perceived thirst existed in T (7 ± 2 on a 1–9 scale) than NT (4 ± 2, P  < 0.001) after the TT . No significant differences in power output existed during the TT between hydration ( EU 202.9 ± 36.5  W vs DH 207.0 ± 35.9  W , P  = 0.362) and thirst conditions ( NT 203.3 ± 35.6  W vs T 206.6 ± 36.8  W , P  = 0.548), nor were there differences in completion time ( P  = 0.832) or pacing profile ( P  = 0.690). Within the range of up to 3% body mass loss, neither the physiologic effects from lowered hydration status nor the perception of thirst, separately or combined, affected sustained submaximal exercise performance in the heat for a healthy and fit population.