Body Mapping of Sweating Rate and Sweat Sodium Concentration in Athletes during Moderate Intensity Exercise: Relation between Local and Whole Body
Authors: Baker Lindsay B. , Barnes Kelly A. , Ungaro Corey T. , Sopeña Bridget C. , Nuccio Ryan P. , Reimel Adam J. , Stofan John R. , Carter James M. 
Published: November 2023

The absorbent patch method is often used to estimate whole body (WB) sweating responses in athletes. However, no study havs investigated the relation between results obtained with the local absorbent patch method (L) versus WB for both sweating rate (SR) and sweat sodium concentration ([Na+]). Therefore, the objective of this study was to determine the relation between LSR and WBSR as well as local and WB sweat [Na+] during moderate intensity exercise. Thirteen non‐heat acclimated, male, recreational athletes (age: 31 ± 6 y; BSA: 1.88 ± 0.18 m2; VO2max: 51±8 ml/kg/min) completed 90 min of moderate intensity cycling (75–85% maximal heart rate) in a warm environment (30°C, 41% relative humidity) to determine WB sweat [Na+] using the washdown technique. In addition, small sweat samples were collected from the dorsal and ventral forearm, tricep, chest, scapula, lower back, ventral thigh, calf, and forehead with absorbent patches (3M TegadermTM+Pad; pad size 10 cm2) and analyzed via ion chromatography to determine local sweat [Na+]. WBSR was determined from body mass change over time corrected for fluid intake, urine output, respiratory water loss, and metabolic mass loss. LSR was determined from the mass change in the absorbent pad and the duration of pad time on the skin. A linear regression analysis and Pearson product moment correlation were used to determine the relation between LSR versus WBSR and local versus WB sweat [Na+]. A repeated‐measures one‐way ANOVA with Dunnett post hoc test was used to determine differences between LSR and WBSR as well as local and WB sweat [Na+]. Data are shown as mean ± SD. WBSR and WB sweat [Na+] were 0.63 ± 19 mg/cm2/min and 40 ± 14 mmol/L, respectively. LSR and local sweat [Na+] from all nine anatomical sites were significantly correlated with WBSR (r2: 0.43–0.71, p < 0.05) and WB sweat [Na+] (r2: 0.59–0.82, p < 0.01), respectively. There was no difference between calf LSR (0.73 ± 31 mg/cm2/min) and WBSR. For all other anatomical sites LSR was significantly greater than WBSR (by +0.34 ± 0.25 mg/cm2/min (thigh) to +3.86 ± 2.86 mg/cm2/min (forehead), p < 0.001). With respect to sweat [Na+], ventral forearm, dorsal forearm, thigh, calf, and lower back were not different than WB (36 ± 20 mmol/L (calf) to 50 ± 24 mmol/L (lower back)). However, local sweat [Na+] from the scapula, tricep, forehead, and chest were significantly greater than WB sweat [Na+] (by +12 ± 11 mmol/L (tricep) to +31 ± 16 mmol/L (scapula), p < 0.001). In conclusion, while many local sites overestimated WB sweating responses, there were significant correlations between LSR and WBSR as well as local and WB sweat [Na+] at all nine anatomical sites tested. In general, it seems that the limbs (e.g., dorsal and ventral forearms, ventral thigh, and calf) are the most representative of WBSR and WB sweat [Na+]. These results can help inform sweat testing best practices in non‐heat acclimated, male, recreational athletes during moderate exercise in a warm environment.Support or Funding InformationThis study was funded by the Gatorade Sports Science Institute, a division of PepsiCo, Inc. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc.