Expanded prediction equations of human sweat loss and water needs

Abstract

Gonzalez RR, Cheuvront SN, Montain SJ, Goodman DA, Blanchard LA, Berglund LG, Sawka MN. Expanded prediction equations of human sweat loss and water needs. J Appl Physiol 107: 379 -388, 2009. First published April 30, 2009 doi:10.1152/japplphysiol.00089.2009.-The Institute of Medicine expressed a need for improved sweating rate (ṁ sw) prediction models that calculate hourly and daily water needs based on metabolic rate, clothing, and environment. More than 25 years ago, the original Shapiro prediction equation (OSE) was formulated as ṁ sw, where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment; OSE was developed for a limited set of environments, exposures times, and clothing systems. Recent evidence shows that OSE often overpredicts fluid needs. Our study developed a corrected OSE and a new ṁ sw prediction equation by using independent data sets from a wide range of environmental conditions, metabolic rates (rest to Յ450 W/m 2 ), and variable exercise durations. Whole body sweat losses were carefully measured in 101 volunteers (80 males and 21 females; Ͼ500 observations) by using a variety of metabolic rates over a range of environmental conditions (ambient temperature, 15-46°C; water vapor pressure, 0.27-4.45 kPa; wind speed, 0.4 -2.5 m/s), clothing, and equipment combinations and durations (2-8 h). Data are expressed as grams per square meter per hour and were analyzed using fuzzy piecewise regression. OSE overpredicted sweating rates (P Ͻ 0.003) compared with observed ṁ sw. Both the correction equation (OSEC), ṁ sw ϭ 147 ⅐ exp (0.0012 ⅐ OSE), and a new piecewise (PW) equation, ṁ sw ϭ 147 ϩ 1.527 ⅐ Ereq Ϫ 0.87 ⅐ Emax were derived, compared with OSE, and then cross-validated against independent data (21 males and 9 females; Ͼ200 observations). OSEC and PW were more accurate predictors of sweating rate (58 and 65% more accurate, P Ͻ 0.01) and produced minimal error (standard error estimate Ͻ 100 g ⅐ m Ϫ2 ⅐ h Ϫ1 ) for conditions both within and outside the original OSE domain of validity. The new equations provide for more accurate sweat predictions over a broader range of conditions with applications to public health, military, occupational, and sports medicine settings. thermoregulation; modeling; fluid balance; hydration; fluid replacement DAILY WATER NEEDS can be determined from "minimal" water losses and expected increases in different water flux avenues (11,22). Metabolic water production and respiratory losses often offset each other, and fecal losses are usually small (11,22). Urinary losses primarily depend on hydration status and osmolar load, but sweat represents the largest potential avenue of body water loss. Knowledge of sweat losses is therefore critical for calculating water needs for active populations, particularly when exposed to heat stress (11,22). For example, military potable water planning relies on water tables generated from existing prediction equations (15, 25), and similar nomograms have been generated for public health purposes (11). Al...

Skin temperature modifies the impact of hypohydration on aerobic performance

“…This means that athletes, military personnel, and occupational workers who experience skin warming (ambient conditions, wearing protective clothing or body armor) are more susceptible to negative effects of hypohydration on performance. Therefore, rehydration should be stressed more with increasing heat stress conditions, not simply because of greater sweat rates (13) and potential for incurring a water deficit (34), but because hyperthermia (particularly warm skin) accentuates the performance decrement from a given water deficit. Our approach of employing graded compensable heat stress avoided potential confounders of alternative approaches and allowed for the examination of the role of T sk in aerobic exercise performance.…”

Sweat loss prediction using a multi-model approach

“…In the Gonzalez equation, the sweat rate is also a function of E req and E max , and is lineally proportional to E req and inversely proportional to E max . The corrected Shapiro equation and the new Gonzalez equation were reported to be more accurate than the original Shapiro equation (Gonzalez et al 2009). It should be noted that, although these empirical equations all appear to be straightforward, the derivations of E req and E max are not simple.…”

“…Sweat loss is influenced by the physical and physiological conditions near or at the skin surface, including environmental conditions, clothing properties, metabolic heat production, and hydration status. Several empirical equations have been developed to predict sweat losses (Nadel et al 1971;Shapiro et al 1982;International Organization for Standardization 1989;Gonzalez et al 2009). In the Shapiro equation, sweat loss is expressed as a simple function of the required evaporation rate (E req ) and the maximal evaporation rate (E max ) (Shapiro et al 1982).…”

“…These data were collected during 2-h exposures to various environmental conditions (ambient temperature 20-54°C, relative humidity 10-90%), with test volunteers walking at three steady-state metabolic rates and wearing different ensembles (Shapiro et al 1982). A method to correct the Shapiro equation and a new sweat equation were developed by using independent datasets from a wide range of environmental conditions, metabolic rates, and variable exercise durations (Gonzalez et al 2009). In the Gonzalez equation, the sweat rate is also a function of E req and E max , and is lineally proportional to E req and inversely proportional to E max .…”

Systematic Review Focusing on the Excretion and Protection Roles of Sweat in the Skin

“…In 2005, the US Dietary Reference Intake standards for water and electrolytes set by the Institute of Medicine used the original Shapiro equation to estimate the rate of sweating, calculate daily water requirements and evaluate what is the necessary supplementary amount of Na under a broad range of activity levels and environmental conditions. Later, some scholars amended this formulation according to the basal metabolism rate, climatic conditions, clothing and other factors [11]. Yet the factors accounting for water metabolism are not completely clear yet.…”