Article

Hypohydration impairs endurance exercise performance in temperate but not cold air

US Army Research Institute of Environmental Medicine, Thermal and Mountain Medicine Division, Kansas St., Natick, MA 01760-5007, USA.
Journal of Applied Physiology (Impact Factor: 3.06). 11/2005; 99(5):1972-6. DOI: 10.1152/japplphysiol.00329.2005
Source: PubMed

ABSTRACT

This 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 = 24 +/- 6 yr, height = 170 +/- 6 cm, weight = 72.9 +/- 11.1 kg, peak O2 consumption = 48 +/- 9 ml.kg(-1).min(-1)) were exposed to 3 h of passive heat stress (45 degrees 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 degrees C) or temperate (20 degrees 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 perceived 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 < 0.05). Heart rate was significantly higher at 30 min within the temperate trial (HYP > EUH) and at 60 min within the cold trial (HYP > EUH) (P < 0.05). Ratings of perceived 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 < 0.05) for HYP than EUH in the temperate trials. The corresponding change in performance (EUH-HYP) was greater for temperate (-8%) than for cold (-3%) (P < 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.

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    • "To examine the prevailing theory that the interaction of skin temperature, core temperature, and hypohydration have adverse effects on exercise performance; several investigators examined the effect of high skin vs high core temperature with and without dehydration on exercise performance. Cheuvront et al. (2005) tested the effect of hypohydration on aerobic performance utilizing a protocol of 30 min exercise at ∼50% , followed by a 30 min time trial in temperate and cold environments. A small 3% body mass loss (5% body water loss) impaired performance by 8% in the temperate (T sk ∼29°C) but not in the cold environment (T sk ∼20°C). "
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    • "As individuals become dehydrated this puts further strain on the cardiovascular system due to an increase in heart rate, diminished plasma volume, stroke volume and cardiac *Address correspondence to this author at the Faculty of Health and Science, Medical and Sports Sciences, University of Cumbria Bowerharm Road, Lancaster, LA1, UK; Tel: +44 1524 590839; Fax: +44 1524 384385; E-mail: susan.dewhurst@cumbria.ac.uk output, reducing venous return and cardiac filling during both exercise and rest [7] [8] [9]. Furthermore, dehydration inhibits thermoregulatory control due to alterations in sweat rate and blood flow. "
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