Medicine & Science in Sports & Exercise:
A-23 Thematic Poster - Thermoregulation: Sweating: JUNE 1, 2011 9:30 AM - 11:30 AM: ROOM: 304
Ely, Matthew R.1; Kenefick, Robert W. FACSM1; Cheuvront, Samuel N. FACSM1; Chinevere, Troy D.1; Lacher, Craig P.2; Lukaski, Henry C. FACSM2; Montain, Scott J. FACSM1
1USARIEM, Natick, MA. 2USDA, Grand Forks, ND.
(No relationships reported)
Initial sweat is concentrated in minerals and becomes dilute with serial measures during exercise in the heat. Possible causes of decreasing sweat mineral concentrations include reduced dermal mineral concentrations surrounding the sweat duct or flushing of surface contamination.
PURPOSE: To simultaneously sample mineral concentrations in transdermal fluid (TDF), sweat, and serum during extended exercise-heat stress to characterize the serial changes in sweat mineral concentrations.
METHODS: Sixteen heat-acclimated individuals (14M, 2F) walked on a treadmill (1.56m·s-1, 3.0% grade) in a 35°C, 20% RH, 1 m·s-1 wind environment 50 min each hour for 3-hours. Mineral concentrations (Ca, Cu, Fe, K, Mg, Na and Zn) were measured each hour from blood serum and sweat from upper back (sweat pouch) and arm (bag). Additionally, TDF was sampled hourly from the upper back dermal space surrounding the sweat pouch. Collection sites were meticulously cleaned using surgical scrub brushes and distilled water (18MΩ) to minimize surface contamination. Mineral concentrations were determined by inductively coupled argon plasma emission spectrometry.
RESULTS: There was a modest increase in TDF Fe (15%) and decrease in TDF Zn (-18%) while all other mineral concentrations in TDF, serum, and upper back sweat remained stable over time. The alterations in TDF Fe and Zn occurred without concomitant changes in sweat Fe and Zn concentrations from the pouch. In contrast, the initial arm bag sweat mineral concentrations were greater than those measured in the sweat pouch. Arm bag Ca, Cu, Mg, and Zn concentrations declined 26 to 76% from initial to the subsequent samples, becoming similar to sweat pouch concentrations from the upper back.
CONCLUSION: The alterations in Fe and Zn TDF concentrations occurred without variations to mineral concentrations from the sweat pouch. After prolonged sweating, the elevated mineral concentrations measured in the arm bag decreased and became similar to those measured in the sweat pouch. It is concluded that the initially concentrated sweat measured in the arm bag was due to surface contamination that could not be thoroughly cleaned (e.g. fingernails, arm hair) and nominal TDF mineral shifts do not affect sweat mineral concentrations.