Body map of regional vs. whole body sweating rate and sweat electrolyte concentrations in men and women during moderate exercise-heat stress

Abstract

This study determined the relations between regional (REG) and whole body (WB) sweating rate (RSR and WBSR, respectively) as well as REG and WB sweat Na concentration ([Na]) during exercise. Twenty-six recreational athletes (17 men, 9 women) cycled for 90 min while WB sweat [Na] was measured using the washdown technique. RSR and REG sweat [Na] were measured from nine regions using absorbent patches. RSR and REG sweat [Na] from all regions were significantly ( P < 0.05) correlated with WBSR ( r = 0.58-0.83) and WB sweat [Na] ( r = 0.74-0.88), respectively. However, the slope and y-intercept of the regression lines for most models were significantly different than 1 and 0, respectively. The coefficients of determination ( r) were 0.44-0.69 for RSR predicting WBSR [best predictors: dorsal forearm ( r = 0.62) and triceps ( r = 0.69)] and 0.55-0.77 for REG predicting WB sweat [Na] [best predictors: ventral forearm ( r = 0.73) and thigh ( r = 0.77)]. There was a significant ( P < 0.05) effect of day-to-day variability on the regression model predicting WBSR from RSR at most regions but no effect on predictions of WB sweat [Na] from REG. Results suggest that REG cannot be used as a direct surrogate for WB sweating responses. Nonetheless, the use of regression equations to predict WB sweat [Na] from REG can provide an estimation of WB sweat [Na] with an acceptable level of accuracy, especially using the forearm or thigh. However, the best practice for measuring WBSR remains conventional WB mass balance calculations since prediction of WBSR from RSR using absorbent patches does not meet the accuracy or reliability required to inform fluid intake recommendations. NEW & NOTEWORTHY This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concentrations and determined the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat Na concentration from REG, especially using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations.

Physiology of sweat gland function: The roles of sweating and sweat composition in human health

“…[146,147]. This concept is illustrated in Figure 8, which shows a significant correlation (r = 0.71, p < 0.05) between mean regional sweating rate and mean sweat [Na] across eight different regions, where sweat [Na] ranged from 36 mmol/L on the calf (lowest sweating rate) to 72 mmol/L on the scapula (highest sweating rate) [149].…”

“…• Creates microenvironment (increases local skin temperature and humidity) [362] and can alter regional sweating rate compared with uncovered skin [370,410] • Absorbent pad may introduce background contamination [149,286] • Potentially any constituent impacted by changes in RSR (Na, Cl, HCO…”

“…• Background Na, Cl, Ca, Mg, Cu, Mn, Fe, Zn reported in patches [149,286] • Limit duration of patch on skin and remove well before saturation [411] • Contaminants from the environment cannot penetrate adhesive barrier (Tegaderm TM ) so can be worn during normal activities, including exercise and swimming [412].…”

“…Regional sweat [Na] typically ranges from 10 to 90 mmol/L ( Figure 5(a); see also [144][145][146][147][148]), while whole-body sweat [Na] is 20-80 mmol/L (predicted shown in Figure 5(b); measured in references [144,146,147,149]). The range in sweat [Cl] is similar, but perhaps slightly lower than that of sweat [Na], with whole-body values reported to be~20-70 mmol/L [134,144,149]. Table 1 shows the host and environmental factors that account for some of the variability in sweat Na ion reabsorption is controlled by Na-K-ATPase activity, which is influenced by plasma aldosterone concentration and/or sweat gland sensitivity to aldosterone.…”

“…Correlations between sweating rate and sweat [Na] were not significant (p > 0.05). Reprinted from Baker et al 2018 [149] with permission. micronutrients, lactate, heavy metals, or environmental toxicants.…”