title: Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake.
abstract: This investigation examined the distinct and interactive effects of initial hydration state, exercise-induced dehydration, and water rehydration in a hot environment. On four occasions, 10 men performed a 90-min heat stress test (treadmill walking at 5.6 km/h, 5% grade, 33 degrees C, 56% relative humidity). These heat stress tests differed in pretest hydration [2 euhydrated (EU) and 2 hypohydrated (HY) trials] and water intake during exercise [2 water ad libitum (W) and 2 no water (NW) trials]. HY+NW indicated greater physiological strain than all other trials (P < 0.05-0.001) in heart rate, plasma osmolality (Posm), sweat sensitivity (g/degrees C.min), and rectal temperature. Unexpectedly, final HY+W and EU+W responses for rectal temperature, heart rate, and Posm were similar, despite the initial 3.9 +/- 0.2% hypohydration in HY+W. We concluded that differences in pretest Posm (295 +/- 7 and 287 +/- 5 mosmol/kg for HY+W and EU+W, respectively) resulted in greater water consumption (1.65 and 0.31 liter for HY+W and EU+W, respectively), no voluntary dehydration (0.9% body mass increase), and attenuated thermal and circulatory strain during HY+W.
authors.affiliation: Human Performance Laboratory, University of Connecticut, Storrs 06269-1110, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Armstrong
authors.forename: C M
authors.initials: CM
authors.lastname: Maresh
authors.forename: C V
authors.initials: CV
authors.lastname: Gabaree
authors.forename: J R
authors.initials: JR
authors.lastname: Hoffman
authors.forename: S A
authors.initials: SA
authors.lastname: Kavouras
authors.forename: R W
authors.initials: RW
authors.lastname: Kenefick
authors.forename: J W
authors.initials: JW
authors.lastname: Castellani
authors.forename: L E
authors.initials: LE
authors.lastname: Ahlquist
mesh_terms: D000328:Adult; D001775:Blood Circulation; D001831:Body Temperature; D001834:Body Water / Q000378:metabolism*; D003681:Dehydration / Q000503:physiopathology*; D004326:Drinking; D015444:Exercise; D006358:Hot Temperature; D006801:Humans; D008297:Male; D013312:Stress, Physiological / Q000503:physiopathology