Skin temperature modifies the impact of hypohydration on aerobic performance

Abstract

Kenefick RW, Cheuvront SN, Palombo LJ, Ely BR, Sawka MN. Skin temperature modifies the impact of hypohydration on aerobic performance. J Appl Physiol 109: 79 -86, 2010. First published April 8, 2010 doi:10.1152/japplphysiol.00135.2010.-This study determined the effects of hypohydration on aerobic performance in compensable [evaporative cooling requirement (E req) Ͻ maximal evaporative cooling (E max)] 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 (T a). Our hypothesis was that 4% hypohydration would impair aerobic performance to a greater extent with increasing heat stress. Thirty-two men [22 Ϯ 4 yr old, 45 Ϯ 8 ml·kg Ϫ1 ·min Ϫ1 peak O2 uptake (V O2peak)] were divided into four matched cohorts (n ϭ 8) and tested at one of four T a in euhydrated (EU) and hypohydrated (HYPO, Ϫ4% body mass) conditions. Subjects completed 30 min of preload exercise (cycle ergometer, 50% V O2peak) followed by a 15 min self-paced time trial. Timetrial performance (total work, change from EU) was Ϫ3% (P ϭ 0.1), Ϫ5% (P ϭ 0.06), Ϫ12% (P Ͻ 0.05), and Ϫ23% (P Ͻ 0.05) in 10°C, 20°C, 30°C, and 40°C T a, respectively. During preload exercise, skin temperature (T sk) increased by ϳ4°C per 10°C Ta, while core (rectal) temperature (T re) values were similar within EU and HYPO conditions across all T a. A significant relationship (P Ͻ 0.05, r ϭ 0.61) was found between T sk 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 T a. Our conclusions are as follows: 1) hypohydration degrades aerobic performance to a greater extent with increasing heat stress; 2) when T sk is Ͼ29°C, 4% hypohydration degrades aerobic performance by ϳ1.6% for each additional 1°C T sk; 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. dehydration; total work; graded ambient temperature; cutaneous blood flow; mean arterial pressure HYPOHYDRATION (Ͼ2% body mass) degrades aerobic performance in temperate and warm-hot conditions (34, 37); however, there is little knowledge of the relative impact of different environmental conditions on aerobic performance at a given level of hypohydration. Cheuvront and colleagues (3) demonstrated that 3% hypohydration did not alter aerobic performance (time trial) in cold (2°C) conditions but reduced aerobic performance in temperate (20°C) conditions. Several reviews speculate (6, 35) that hypohydration might degrade aerobic performance more in warm-hot than temperate conditions. If this is true, then it is also possible that hypohydration might degrade aerobic performance more in hot than warm conditions. While this is plausible, the impact of hypohydration on aerobic exercise performance along a continuum of air temperatures has not been experimentally evalua...

Electrolyte supplementation during severe energy restriction increases exercise capacity in the heat

“…It is well known that the effects of hypohydration on exercise performance are more profound in hot than temperate environments (Kenefick et al 2010). The present study implicates the hypohydration and reduced plasma volume observed during severe ER with fatigue during exercise, at least in the heat.…”

“…This hypohydration appears to be caused by the continued excretion of electrolytes in urine, despite little or no intake (James and Shirreffs 2013), and might be offset by electrolyte supplementation during severe ER (Consolazio et al 1968a). Hypohydration reduces endurance capacity and performance (Cheuvront and Kenefick 2014), an effect that is exacerbated as environmental temperature increases (Kenefick et al 2010). Therefore, the hypohydration, and particularly plasma volume reduction, that accompanies severe ER might negatively impact on exercise capacity (Cheuvront and Kenefick 2014), particularly if exercise is undertaken in a hot environment.…”

Cold Stress Effects on Exposure Tolerance and Exercise Performance

“…They found that with skin-surface cooling, the operating point of the PCWP-SV curve was shifted to the right onto the flatter part of the hyperbolic curve. Even when dehydrated up to 4% body mass, cold exposure (8 • C air) maintains stroke volume during 30-min of exercise at 72% VO 2max (108), leading to no change in cardiac output (Q); this is likely related to the relatively small changes in exercise performance when dehydrated in cool to cold, versus warm, environments (43,142). Cardiac output during exercise in the cold is dependent on exercise intensity.…”

Insulated skin temperature as a measure of core body temperature for individuals wearing CBRN protective clothing

“…Above a certain threshold, thermoregulatory responses are evoked (Johnson and Park, 1982), including cutaneous vasodilation which promotes an increase in skin blood flow for dry heat loss from the skin to the environment. The extent to which T s and T re converge (ranging from 0.1 °C to 1.5 °C in the current study) depends upon the temperature of the microclimate (Kenefick et al, 2010), but once thermal equilibrium between the two measures is reached, T re and T s should rise in parallel. In GTS and PRPS, T is and T re converged for the first 20 to 30 min of exercise, after which they increased in parallel for the remainder of the trial.…”

“…This was also shown by McLellan et al (1993) where the difference between T re and mean T s was 1.3 °C and 2.2 °C when ambient temperatures were 30 °C and 18 °C, respectively, for firefighters carrying out heavy work in CBRN PPE. Microclimate temperature clearly has a direct impact on the degree to which T is and T re converge (McLellan et al, 1993, Kenefick et al, 2010, and the inclusion of T mc in the equation (equation 3) improves the prediction of T re . However, T mc is subtracted, or inversely in the equation, which is counterintuitive based on the assumption that as T mc increases, capacity for heat loss decreases, which is likely to result in an increase in T re .…”