Skin temperature modifies impact of hypohydration on aerobic performance

US Army Research Institute of Environmental Medicine, Thermal and Mountain Medicine Division, Kansas St., Natick, MA 01760, USA.
Journal of Applied Physiology (Impact Factor: 3.43). 04/2010; 109(1):79-86. DOI: 10.1152/japplphysiol.00135.2010
Source: PubMed

ABSTRACT This study determined the effects of hypohydration on aerobic performance in compensable [evaporative cooling requirement (Ereq) < maximal evaporative cooling (Emax)] conditions of 10°C [7°C wet bulb globe temperature (WBGT)], 20°C (16°C WBGT), 30°C (22°C WBGT), and 40°C (27°C WBGT) ambient temperature (Ta). Our hypothesis was that 4% hypohydration would impair aerobic performance to a greater extent with increasing heat stress. Thirty-two men [22 ± 4 yr old, 45 ± 8 ml·kg-1peak O2 uptake (Vo2Peak)] were divided into four matched cohorts (n = 8) and tested at one of four T a in euhydrated (EU) and hypohydrated (HYPO, -4% body mass) conditions. Subjects completed 30 min of preload exercise (cycle ergometer, 50% Vo2peak) followed by a 15 min self-paced time trial. Timetrial performance (total work, change from EU) was -3% (P = 0.1), -5% (P = 0.06), -12% (P < 0.05), and -23% (P < 0.05) in 10°C, 20°C, 30°C, and 40°C Ta, respectively. During preload exercise, skin temperature (Tsk) increased by ∼4°C per 10°C Ta, while core (rectal) temperature (Tre,) values were similar within EU and HYPO conditions across all Ta. A significant relationship (P < 0.05, r = 0.61) was found between Tsk and the percent decrement in time-trial performance. During preload exercise, hypohydration generally blunted the increases in cardiac output and blood pressure while reducing blood volume over time in 30°C and 40°C Ta. Our conclusions are as follows: 1) hypohydration degrades aerobic performance to a greater extent with increasing heat stress; 2) when TSk is >29°C, 4% hypohydration degrades aerobic performance by ∼1.6% for each additional 1°C Tsk; and 3) cardiovascular strain, from high skin blood flow requirements combined with blood volume reductions induced by hypohydration is an important contributor to impaired performance.Copyright © 2005 by the American Physiological Society Skin temperature modifies the impact of hypohydration on aerobic performance.

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Available from: Brett R Ely, Mar 17, 2014
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    • "Dr. Sam Cheuvront (see Figure 1) is developing (with industrial partners) technologies for a valid non-invasive hydration status measure. We believe that exercise performance in the heat is impaired because of high skin blood flow requirements [15] and hypovolemia [16] via the cardiovascular system rather than a “critical core temperature” as is a popular belief in the sports medicine literature [17]. Drs. Bob Kenefick and Nisha Charkoudian (see Figure 1) are continuing research to determine if blood pressure control (challenged by vasodilation and hypovolemia) provides the critical signals for impairing exercise-heat performance. "
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    ABSTRACT: This invited autobiography reviews the career of Michael N. Sawka. Influences: Dr. Sawka soon will retire after a 40-year research career and was influenced by great professors, mentors and colleagues. Career Path: After working at the Dayton Veterans Administration Medical Center and Wright State University, Dr. Sawka's remaining 32 years were at the US Army Research Institute of Environmental Medicine. Research Story: His primary research thrusts included: 1) physiology of upper body exercise; 2) blood volume and its impact on thermoregulation and performance; 3) hydration and its impact on thermoregulation and performance 4) heat stress physiology - adaptations / maladaptations and performance. Summary: His career highlights were the personal interactions, intellectual excitement and satisfaction of producing knowledge that will be "tested by time".
    11/2012; 1(1):10. DOI:10.1186/2046-7648-1-10
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    • "Despite EC's lack of an ergogenic effect, the current study and previous research (Kenefick et al., 2010; Tyler et al., 2010; Tyler & Sunderland, 2011a, b) suggest that performance might benefit from externally cooling the skin with cold water during sustained lower intensity exercise. Variables in the present study affected by EC (T sk , thermal perception, and RPE) and drinking (HR, and thirst perception) generally failed to overlap, indicating that combined drinking and EC might act additively or synergistically to improve performance during low-intensity exercise. "
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    ABSTRACT: Only limited research evaluates possible benefits of combined drinking and external cooling (by pouring cold water over the body) during exercise. Therefore, this study examined cold water drinking and external cooling on physiological, perceptual, and performance variables in hot, dry environments. Ten male runners completed four trials of walking 90 min at 30% VO(2max) followed by running a 5-km time trial in 33 ± 1 °C and 30 ± 4% relative humidity. Trials examined no intervention (CON), oral rehydration (OR), external cooling (EC), and oral rehydration plus external cooling (OR + EC). Investigators measured rectal temperature, skin temperatures, heart rate, thirst, thermal sensation, and ratings of perceived exertion (RPE). Oral rehydration (OR and OR + EC) significantly lowered heart rate (P < 0.001) and thirst (P < 0.001) compared with nondrinking (CON and EC) during low-intensity exercise. External cooling (EC and OR + EC) significantly reduced chest and thigh temperature (P < 0.001), thermal sensation (P < 0.001), and RPE (P = 0.041) compared with non-external cooling (CON and OR) during low-intensity exercise. Performance exhibited no differences (CON = 23.86 ± 4.57 min, OR = 22.74 ± 3.20 min, EC = 22.96 ± 3.11 min, OR + EC = 22.64 ± 3.73 min, P = 0.379). Independent of OR, pouring cold water on the body benefited skin temperature, thermal sensation, and RPE during low-intensity exercise in hot, dry conditions but failed to influence high-intensity performance.
    Scandinavian Journal of Medicine and Science in Sports 08/2012; 22(6). DOI:10.1111/j.1600-0838.2012.01510.x · 3.17 Impact Factor
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    • "Moreover, a narrowing T re À " T sk gradient has been proposed to enhance whole body skin blood flow requirements, which leads to a decrement in _ VO 2 max and increase in relative exercise intensity (Kenefick et al. 2010). The T re À " T sk gradients noted under heat stress in the present study are consistent with those previously suggested to reduce central blood volume and potentially compromise cerebral and muscle perfusion (Cheuvront et al. 2010; Kenefick et al. 2010). However, a reduction in cerebral perfusion is associated with an enhanced cerebral metabolic rate for oxygen, as well as glucose and lactate uptake during maximal exercise (González-Alonso et al. 2004). "
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