Sweat and Sodium Losses During Practice in Professional Football Players

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Relatively few studies exist to characterize risk factors related to player safety, heat stress, and dehydration in professional football during on-field conditions. PURPOSE: Todescribesweatloss, dehydration, fluidintake, andsweatsodiumlossesduringon - fieldconditions. METHODS: We measured sweat loss and fluid intake in 16 NFL players and sweat sodium (s[Na+]) in a subset of the players (n = 13) during three practices in different US regions. Practices lasted about two hours during pre-season training camps. Change in bodyweight, corrected for fluid intake and urine loss, was used to estimate gross sweat loss. An arm-bag collection technique that excluded sweat from the hand was used to estimate whole-body s[Na+] values. Voluntary fluid intake (water and sports drinks) was measured by recording pre- and post-practice bottle weights. RESULTS: Conditions ranged from 12–31 °C WBGT. Practices were conducted in both partial and full gear. Gross sweat loss ranged from 1.3–5.2 liters per hour with s[Na+] ranging 513–2330 mg per liter (22–101 mEq/L). This resulted in total s[Na+] losses between 0.8–9.9 grams during the practices. Fluid intake ranged from 0.3–5.0 liters and resulted in replacing as little as 16% and as much as 120% of sweat losses. Average dehydration was 1.2 ± 1.0% of initial bodyweight. Players showed large interindividual variability in sweat loss, fluid intake and s[Na+]. CONCLUSION: The extent to which factors of environment, volume of work, or gear influenced fluid and total sodium loss could not be determined because training intensity and work volume were not standardized. Nonetheless, these data confirm that large fluid and sodium losses occur during pre-season practices. Often, little fluid is replaced. Long practices in full uniform and in hot, humid conditions appeared to increase the risk for larger sweat and sodium losses.