Effect Of Different Exercise Environments On Sweat Metrics In Cross-country Athletes

: Sweat rate (SR) and sodium loss from exercise have been shown to vary between individuals. Previous research has focused on developing normative data without accounting for environmental factors that may influence sweat metrics. Thus, the current study investigated the impact of different environmental conditions on sweat metrics in a homogenous group. PURPOSE: To examine the effect of different exercise environments on SR and sweat sodium concentration ([Na+]) during a prolonged low-intensity exercise in male DII cross-country runners. METHODS: Four male collegiate cross-country runners performed a 50-minute low-intensity exercise protocol (7:00-7:30 per mile running pace) on an outdoor track (25.6 °C, 11% humidity) and in an indoor gym (21.1 °C, 29% humidity). SR was calculated from pre- to post-exercise change in body mass. A sweat patch was used to measure regional sweat [Na+]. Height, body composition, and urine specific gravity (USG) were also measured. RESULTS: Sweat metrics between the outdoor and indoor environment were significantly different (p < .05) in absolute SR (1.62 ± 0.18 L · h-1, 1.17 ± 0.13 L · h-1; p < .002), SR relative to body mass (24.84 ± 2.58 ml · kg-1 · h-1, 17.95 ± 1.41 ml · kg-1 · h-1; p < .003), SR relative to fat-free mass (29.92 ± 2.42 ml · kg-1 · h-1, 19.44 ± 1.73 ml · kg-1 · h-1; p < .001), and regional sweat [Na+] (1672.50 ± 500.27 ppm, 1212.50 ± 288.04 ppm; p < .02), respectively. There was a significant difference in USG (p < .04) in the outdoor environment (1.007 ± .003 units) and the indoor environment (1.023 ± .013 units). There was also a significant correlation in SR relative to body mass and whole-body sweat (WBS) [Na+] for the outdoor and indoor environments (1298.74 ± 306.96 ppm, 1099.98 ± 260.54 ppm) (r2 > .65) respectively, as well as SR relative to body surface area and WBS [Na+] for both environments (r2 > .65). CONCLUSIONS: Exercise in a warmer outdoor environment is associated with a higher SR and sweat [Na+] compared to an indoor environment. The correlation between SR and WBS [Na+] paired with the difference in SR found between the testing environments suggests that sodium loss from exercise may follow an exponential trend in response to increasing temperature.