Sweat Electrolyte Content and Fluid Balance in Elite Triathletes

ABSTRACT Elite triathletes’ sweat volume and electrolyte losses during exercise can be detrimental in a warm environment. PURPOSE: The aim of this study was to investigate urine and sweat electrolyte losses of male and female triathletes during endurance exercise in a warm environment. METHODS: Thirty five Timex sponsored triathletes (n = 20♂, 15♀: age 39 ± 12yr, 33 ± 6 yr; height 181 ± 6 cm, 171 ± 6 cm; weight 76.1 ± 7.0 kg, 60.1 ± 5.4 kg; fast half Ironman time 4:30 ± 0:40 hr:min, 5:09 ± 0:32 hr:min, respectively) completed a 43.4 ± 3.8 minute treadmill run or friction resisted cycle ergometer bike at their predicted half Ironman race pace in a heated environment (28.0 ± 0.5 ºC, 27.2 ± 4.9 % relative humidity). Before exercise each subject provided a urine sample and skin fold measures were taken. Percent dehydration was calculated using pre- and post-exercise nude body weights. Whole body wash-down (WBW) was performed using distilled, deionized water to determine sweat electrolyte content. Twenty-four hour urine was collected to calculate sodium and potassium losses. Twenty-four hour diet intake was recorded to calculate net balance. RESULTS: Sweat electrolyte losses during exercise differed between genders. Men had higher sweat rates and sweat loss than women (1.88 ± 0.38 L·h-1 vs 1.34 ± 0.36 L·h-1, p ≤ 0.001; 1.39 ± 0.31 L vs 0.95 ± 0.27 L, p ≤ 0.001), respectively. Men had greater sweat sodium loss (p=0.004; men: 60.3 ± 19.9 mEq vs women: 39.4 ± 19.9 mEq) and a greater rate of sweat sodium loss (p=0.010; 82.4 ± 26.6 mEq·hr-1 vs women: 56.5 ± 30.1 mEq·hr-1). Concentrations of sweat sodium and potassium did not differ between genders. Men had higher urine sodium mass than women (196.2 ± 80.1 mEq vs 117.5 ± 49.5 mEq, respectively, p=0.002). Net Balance differences were not found between male and female intake and loss of fluid and electrolytes. During the 24 hour dietary consumption, women consumed less water than men (3.026 ± 1.216 L vs 4.594 ± 2.824 L, respectively, p=0.036) and Na+ content (3588.7 ± 1004.7 mg vs 5081.2 ± 2277.2 mg, respectively, p=0.017). CONCLUSION: Sweat volume, electrolyte loss, urinary sodium loss and diet intake differed between male and female elite triathletes. When determining fluid and sodium replacement requirements in warm conditions for high level triathletes, men may need to replace more fluids and sodium at greater rates than women to remain homeostatic