Hypohydration effects on thermoregulation during moderate exercise in the cold
Hyperosmotic hypovolemia impairs vasoconstriction during sedentary cold exposure. The purpose of this study was to determine whether hypohydration alters thermoregulation and cardiovascular responses to exercise in cold air. On four occasions, eight males [35.1 (2.7) years, 175.5 (3.1) cm, 73.3 (2.6) kg, 57.2 (2.6) ml kg−1 min−1 maximal oxygen uptake (V̇O2max), 19.6 (2.4)% fat] walked, in t-shirt, shorts, and shoes, at 50% V̇O2max, for 60 min in either a 4°C (Cold) or a 25°C (Temperate) environment in both hypohydrated state (HYPO, −4% body mass) and euhydrated state (EU). During exercise–cold stress, rectal temperature (Tre), mean weighted skin temperature, heart rate (HR), cardiac output (CO), and stroke volume (SV) were measured every 20 min. Mean weighted skin temperature values were not different between HYPO and EU but were lower (P<0.05) in Cold versus Temperate trials. Tre was not different (P>0.05) between HYPO–Cold and EU–Cold. CO and SV were not different within hydration states and were not different between Cold and Temperate trials (P<0.05). HR was not different between HYPO–Cold and EU–Cold. These data demonstrate that moderate intensity exercise in the cold while hypohydrated does not alter metabolic heat production, skin temperatures and heat loss, nor does it increase thermoregulatory and cardiovascular strain.
KeywordsEnvironment Heat production Hypovolemia Vasoconstriction
The authors would like to thank the subjects for their cooperation and participation in the study. Further the authors wish to thank Jenny Klooster, Tara Foley, Timothy King, Sarah Wright, and Lisa Koning for their technical support. The views, opinions and/or findings in this report are those of the authors and should not be construed as official Department of the Army position, policy, or decision unless so designated by other official designation.
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