Purpose: This study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations.
Methods: Eight male subjects walked on a treadmill at 3.5 mph, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5°C on 10 consecutive days in an environmental chamber set at 45°C, 20% relative humidity. Arm sweat samples were collected during the first 30 min of exercise-heat stress on days 1 and 10 using a polyethylene arm glove.
Results: Final core temperature and HR values were significantly lower (P < 0.05) on day 10 versus day 1. Whole-body sweating rates increased by approximately 6% (P = 0.12). Sweat sodium concentration on day 10 (36.22 ± 7.22 mM) was significantly lower than day 1 (54.49 ± 16.18 mM) (P < 0.05). Sweat mineral concentrations of calcium (~29%), copper (~50%), and magnesium (~43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P < 0.05). A trend for lower sweat iron (~75%; P = 0.07) and zinc (~23%; P = 0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration × whole-body sweat rate) were reduced for calcium (~27%), copper (~46%), and magnesium (~42%) (P < 0.05), but not iron (75%) or zinc (~16%) (P > 0.05), from day 1 to day 10.
Conclusion: Exercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium, and may reduce sweat iron and zinc concentrations.
1U.S. Army Research Institute of Environmental Medicine, Natick, MA; and 2USDA ARS Grand Forks Human Nutrition Research Center, Grand Forks, ND
Address for correspondence: Troy D. Chinevere, Ph.D., U.S. Army Research Institute of Environmental Medicine, Bldg. 42, Kansas St., Natick, MA 01760; E-mail: Troy.Chinevere@us.army.mil.
Submitted for publication October 2007.
Accepted for publication December 2007.