Regional vs. Whole-Body Washdown Trace Mineral Concentration in Sweat

Abstract

PURPOSE: This study compared simultaneous whole-body washdown (WBW) and regional skin surface (REG) sweat collections to determine the relation between REG and WBW sweat [Ca], [Mg], [Cu], [Mn], [Fe], and [Zn]. METHODS: Athletes (4 men, 4 women) cycled in a plastic open-air chamber for 90 min in the heat. Prior to exercise, the subject and bike (covered with plastic) were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh, and removed upon saturation. After exercise, the subject and bike were washed with 5 L of 15mM ammonium sulfate solution to collect all sweat minerals and to determine the volume of unevaporated sweat. Control trials were performed to measure mineral contamination in REG and WBW systems. RESULTS: Because background contamination in the collection system was high for WBW Mn, Fe, and Zn, method comparisons were not made for these three minerals. After background removal, WBW sweat [Ca], [Mg], and [Cu] were 44.6±20.1, 9.8±4.8, and 0.125±0.069 mg/L, respectively. 5-site REG (weighted for local sweat rate and body surface area) sweat [Ca] (59.0±15.9 mg/L), [Mg] (14.5±4.8 mg/L), and [Cu] (0.166±0.031 mg/L) were not statistically different from that of WBW sweat (p>0.05). However, no individual REG patch site or the 5-site REG were significantly correlated with or reliable predictors of WBW sweat [Ca] (r=-0.21, p=0.65; ICC=-0.15), [Mg] (r=0.49, p=0.33; ICC=0.27), or [Cu] (r=0.17, p=0.74; ICC=0.09). CONCLUSION: Comparison of REG vs. WBW sweat [Mn], [Fe], and [Zn] is difficult due to contamination in the WBW collection system. Moreover, REG sweat [Ca], [Mg], and [Cu] are not reliable predictors of WBW sweat composition.