Hypohydration impairs endurance exercise performance in temperate but not cold air

Abstract

Cheuvront, Samuel N., Robert Carter III, John W. Castellani, and Michael N. Sawka. Hypohydration impairs endurance exercise performance in temperate but not cold air. J Appl Physiol 99: 1972Physiol 99: -1976Physiol 99: , 2005. First published July 14, 2005; doi:10.1152/japplphysiol.00329.2005This study compared the effects of hypohydration (HYP) on endurance exercise performance in temperate and cold air environments. On four occasions, six men and two women (age ϭ 24 Ϯ 6 yr, height ϭ 170 Ϯ 6 cm, weight ϭ 72.9 Ϯ 11.1 kg, peak O2 consumption ϭ 48 Ϯ 9 ml⅐ kg Ϫ1 ⅐ min Ϫ1 ) were exposed to 3 h of passive heat stress (45°C) in the early morning with [euhydration (EUH)] or without (HYP; 3% body mass) fluid replacement. Later in the day, subjects sat in a cold (2°C) or temperate (20°C) environment with minimal clothing for 1 h before performing 30 min of cycle ergometry at 50% peak O2 consumption followed immediately by a 30-min performance time trial. Rectal and mean skin temperatures, heart rate, and ratings of percieved exertion measurements were made at regular intervals. Performance was assessed by the total amount of work (kJ) completed in the 30-min time trial. Skin temperature was significantly lower in the cold compared with the temperate trial, but there was no independent effect of hydration. Rectal temperature in both HYP trials was higher than EUH after 60 min of exercise, but the difference was only significant within the temperate trials (P Ͻ 0.05). Heart rate was significantly higher at 30 min within the temperate trial (HYP Ͼ EUH) and at 60 min within the cold trial (HYP Ͼ EUH) (P Ͻ 0.05). Ratings of percieved exertion increased over time with no differences among trials. Total work performed during the 30-min time trial was not influenced by environment but was less (P Ͻ 0.05) for HYP than EUH in the temperate trials. The corresponding change in performance (EUH Ϫ HYP) was greater for temperate (Ϫ8%) than for cold (Ϫ3%) (P Ͻ 0.05). These data demonstrate that 1) HYP impairs endurance exercise performance in temperate but not cold air but 2) cold stress per se does not. dehydration; thermoregulation; environment PERSONS EXERCISING IN COLD WEATHER can incur substantial fluid losses (6) and are commonly advised to maintain hydration to avoid cold injury and sustain performance. Despite these assertions, recent research shows that hypohydration (HYP; reduced body water) does not increase the risk of hypothermia or peripheral cold injury (23,24). Similarly, HYP in excess of 2% body mass impairs endurance exercise performance in hot and temperate environments with the magnitude of effect largest in the heat (4, 30). The extent to which this is true in cooler environments is unknown, but there is evidence that the mechanisms for HYP-mediated fatigue in warmer environments are blunted in the cold and may therefore have less impact.Hyperthermia and cardiovascular strain are two major factors implicated in the genesis of HYP-mediated endurance exercise fatigue in hot and temperate environments (4). Both the i...

National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active

“…Abundant research 4,5,19,62,70,74 has documented aerobic performance decrements with hypohydration. Contradictory findings generally involved marginal levels (less than 2%) of hypohydration or a lack of exercise-intensity measures.…”

“…61 Therefore, in temperate and hot environments, performance is decreased when hypohydration is greater than 2% body mass. 181 It has been demonstrated, however, that in cool environments 74 or when thirst is mitigated, 23 aerobic performance can be maintained. Yet consuming fluids according to thirst alone does not maximize performance.…”

Body weight changes in child and adolescent athletes during a triathlon competition

“…Laboratory-based studies are fairly clear in demonstrating that levels of dehydration greater than 2% BW in adults (Cheuvront et al, 2003;Cheuvront et al, 2005;Walsh et al, 1994) and 1%…”

Effect of increased plasma osmolality on cold-induced thirst attenuation

“…In addition, these results demonstrate that this attenuation can be overridden by increasing P osm . While acute dehydration in the cold has not been shown to alter cardiovascular or thermoregulatory function (KeneWck et al 2004b) or exercise performance (Cheuvront et al 2005), chronic voluntary dehydration has been noted as a major problem for individuals during long term exposure to cold and may increase the risk of peripheral cold injury (O'Brien et al 1998). These results have phenomenological importance for understanding thirst regulation in cold environments and potential application in helping to drive thirst sensation and Xuid intake to prevent chronic dehydration when working or exercising in the cold (Freund and Sawka 1996).…”