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


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 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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Available from: Michael N Sawka, Apr 24, 2015
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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: 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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    ABSTRACT: Marching with essential survival equipment is a fundamental military exercise. A consequence of this increased load is an increased risk of dehydration. Dehydration may have fatal consequences in a combat situation where performance must be optimal. This risk can be minimized with an understanding of the additional fluid needs of soldiers marching when loaded compared to unloaded. The aim of this study was to quantify fluid loss caused by marching with a loaded Bergen rucksack and webbing of 33.5 kg for 45 minutes when compared to unloaded carriage in eight healthy male officer cadets (age, 20.5 ± 0.9 years; body mass 80.2 ± 9.2 kg). The findings demonstrate an increased rate of sweat loss (0.6 ± 0.2 L·h -1 to 1.2 ± 0.4 L·h -1 ; p<0.001) and increased average heart rate (105.5 ± 17.7 beats·min -1 to 136.6 ± 28.3 beats·min -1 ; p<0.001) for unloaded and loaded trial respectively. Urine osmolality significantly increased pre-to post-march (p<0.05), however there was no difference in this increase between the loaded and unloaded trial. The present study demonstrated that marching with a loaded rucksack and webbing increased sweat rate by 100% compared to the same march with no additional load. For soldiers to prevent dehydration and the potential detrimental effects on performance, fluid replacement should also be doubled when marching with loading in a temperate environment, however individual differences in sweat rate should be taken into account.
    The Open Sports Sciences Journal 02/2014; 7(1):16-21. DOI:10.2174/1875399X01407010016
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    • "(Within-subjects %CV = (standard deviation PRACT/mean PRACT) 9 100.) A mean %CV for all 32 volunteers was calculated and considered an a priori 'zone of indifference' for determining meaningful changes during trial days (Cheuvront et al. 2005), which are described in detail below. Each familiarization session took place in a *22 °C, 20–30 % RH environment. "
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    ABSTRACT: Equivocal findings have been reported in the few studies that examined the impact of ambient temperature (T (a)) and hypohydration on cognition and dynamic balance. The purpose of this study was to determine the impact of acute exposure to a range of ambient temperatures (T (a) 10-40 °C) in euhydration (EUH) and hypohydration (HYP) states on cognition, mood and dynamic balance. Thirty-two men (age 22 ± 4 years, height 1.80 ± 0.05 m, body mass 85.4 ± 10.8 kg) were grouped into four matched cohorts (n = 8), and tested in one of the four T (a) (10, 20, 30, 40 °C) when EUH and HYP (-4 % body mass via exercise-heat exposure). Cognition was assessed using psychomotor vigilance, 4-choice reaction time, matching to sample, and grammatical reasoning. Mood was evaluated by profile of mood states and dynamic postural balance was tested using a Biodex Balance System. Thermal sensation (TS), core (T (core)) and skin temperature (T (sk)) were obtained throughout testing. Volunteers lost -4.1 ± 0.4 % body mass during HYP. T (sk) and TS increased with increasing T (a), with no effect of hydration. Cognitive performance was not altered by HYP or thermal stress. Total mood disturbance (TMD), fatigue, confusion, anger, and depression increased during HYP at all T (a). Dynamic balance was unaffected by HYP, but 10 °C exposure impaired balance compared to all other T (a). Despite an increase in TMD during HYP, cognitive function was maintained in all testing environments, demonstrating cognitive resiliency in response to body fluid deficits. Dynamic postural stability at 10 °C appeared to be hampered by low-grade shivering, but was otherwise maintained during HYP and thermal stress.
    Arbeitsphysiologie 10/2012; 113(4). DOI:10.1007/s00421-012-2506-6 · 2.19 Impact Factor
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    • "Hypohydration impaired aerobic performance by 12 and 23% when T sk was 33 and 36 • C, respectively. Figure 4 plots the impact of hypohydration on aerobic performance from the preceding three studies (Castellani et al. 2010; Cheuvront et al. 2005; Kenefick et al. 2010). These studies employed similar procedures over a broad range of T sk from 20 to 36 • C. Segmented regression (Vieth, 1989) was used to approximate the statistical T sk threshold for performance impairment using individual study data points (n = 53 paired observations). "
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    ABSTRACT: This paper reviews the roles of hot skin (>35°C) and body water deficits (>2% body mass; hypohydration) in impairing submaximal aerobic performance. Hot skin is associated with high skin blood flow requirements and hypohydration is associated with reduced cardiac filling, both of which act to reduce aerobic reserve. In euhydrated subjects, hot skin alone (with a modest core temperature elevation) impairs submaximal aerobic performance. Conversely, aerobic performance is sustained with core temperatures >40°C if skin temperatures are cool-warm when euhydrated. No study has demonstrated that high core temperature (∼40°C) alone, without coexisting hot skin, will impair aerobic performance. In hypohydrated subjects, aerobic performance begins to be impaired when skin temperatures exceed 27°C, and even warmer skin exacerbates the aerobic performance impairment (-1.5% for each 1°C skin temperature). We conclude that hot skin (high skin blood flow requirements from narrow skin temperature to core temperature gradients), not high core temperature, is the 'primary' factor impairing aerobic exercise performance when euhydrated and that hypohydration exacerbates this effect.
    Experimental physiology 12/2011; 97(3):327-32. DOI:10.1113/expphysiol.2011.061002 · 2.67 Impact Factor
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