Twice a day lacrosse training in temperate conditions results in a negative 24-Hour sodium balance in male and female university lacrosse players

This study measured 24-hour fluid and sodium balance in 27 university lacrosse players (13 males, 14 females; 21 6 1 years). For 24 hours, participants maintained their usual fluid and food intake, completed a weighed food diary, and collected all urine produced. Participants completed 2 bouts of 1.5 hours (males) or 2 hours (females) lacrosse training (16.0 6 3.9C, 62.3 6 11.7% relative humidity) separated by 2–2.5 hours rest. Nude body mass was measured at baseline (0 hour), 24 hours later, before and after training, and corrected for food/fluid consumed and urine/feces produced during training to determine sweat losses. A sweat patch was applied (scapula) and analyzed for sweat sodium concentration. Data are mean 6 standard deviation or median (Q1–Q3), p, 0.05. Sodium balance at 24 hours was negative for both male (20.76 6 1.31 g) and female (20.47 6 0.70 g) players but was not different between sexes (p 5 0.350). Body mass at 0 hour and 24 hours was not different for male (79.99 6 10.02 kg vs 79.69 6 10.15 kg) or female (65.68 6 10.17 kg vs 65.82 6 10.21 kg; both p . 0.05) players. Sweat rates were relatively low and not different between male (0.39 6 0.23 L/h) and female (0.33 6 0.18 L/h; p 5 0.286) players. There was no difference in sweat sodium concentration (male players: 27 (23–28) mmol/L; female players: 27 (23–31) mmol/L; p 5 0.786). Ad libitum drinking, combined with low sweat rates, generally prevented dehydration accruing to a level that might impair performance. Sodium balance deficit was small (;0.61 g) but may require investigation to understand whether daily deficits accumulate.<p></p>