Human Responses to Cold After Repeated Immersion in 20 Deg. C Water

Abstract

Abstract : The relative importance of core vs. skin temperature reduction as a stimulus for cold acclimation (CA), was assessed by evaluating thermoregulatory responses during cold air exposure (90 min, 5 deg C; CAE), cold water immersion (60 min, 20 deg C; CWI), and cold finger immersion (30 min, 4 deg C; CFI), before and after CA. Subjects acclimated for five weeks by completing daily 1-h water immersions (20 deg C) while either seated quietly (RG) or performing leg exercise (EG). The exercise intensity for EG was selected to prevent core temperature from falling during each CA session. CFI was completed immediately following CWI (hypothermic condition, HC); and a second trial on a separate day (normothermic condition, NC). Cold induced vasodilation (CIVD) was not affected by CA, but CIVD was blunted (P less O.05) during HC, compared to NC before and after CA. A more pronounced change in NE (P less O.05) occurred during CAE following CA, consistent with increased sympathetic activation, which could mediate changes in vasomotor response to cold The reduction of core temperature during CA sessions appears to be a necessary stimulus for this acclimation effect. This study also suggests that heat debt, not increased heat flux alone, is the stimulus for developing cold acclimation.