title: Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat.
abstract: 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.
authors.affiliation: Environmental Ergonomics Laboratory, Department of Kinesiology, Brock University, St. Catharines, Canada.
authors.forename: S S
authors.initials: SS
authors.lastname: Cheung
authors.forename: G W
authors.initials: GW
authors.lastname: McGarr
authors.forename: M M
authors.initials: MM
authors.lastname: Mallette
authors.forename: P J
authors.initials: PJ
authors.lastname: Wallace
authors.forename: C L
authors.initials: CL
authors.lastname: Watson
authors.forename: I M
authors.initials: IM
authors.lastname: Kim
authors.forename: M J
authors.initials: MJ
authors.lastname: Greenway
mesh_terms: D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D001642:Bicycling / Q000502:physiology*; D003681:Dehydration / Q000209:etiology / Q000503:physiopathology*; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D013894:Thirst
keywords: Pacing; heat stress; ratings of perceived exertion; thermal perception; voluntary exercise