Voluntary drinking and hydration in trained, heat acclimatized girls exercising in a hot and humid climate
This study examined the effects of beverage composition on the voluntary drinking pattern, body fluid balance and body temperature responses of heat acclimatized trained girls exercising intermittently in outdoor conditions (WBGT 30.9 0.2degC) Twelve trained, heat acclimatized girls (age 10.6 0.2 years) performed three 3 h sessions, each consisting of four 20 min cycling bouts at 60% VO2max, alternating with 25 min rest. One of three beverages was assigned: unflavored water (W) flavored water (FW) or flavored water plus 6% carbohydrate and 18 mmol/l NaCl (CNa) Drinking was ad libitum. Total intake was similar among conditions (W 953.3 107.8 FW 1026.5 138.1; CNa 906.4 107.5 g) A mild hypohydration occurred during the three conditions (W 1.12% FW 0.95% CNa 0.74% BW, P 0.05) Sweat loss, higher than previously reported for sedentary girls, was not different among conditions (W 1,051.5 90.8; FW 979.9 72.8; CNa 1,052.7 52.6 g) The average amount of urine produced (W 269.8 85.9; FW 320.8 87.2; CNa 85.6 9.3 g) was 73 and 68% higher during FW and W, respectively, compared to CNa (CNa vs. FW, P 0.05) The increase in rectal temperature, heart rate and all perceptual variables did not differ among conditions. In conclusion, flavoring of the water and addition of 6% carbohydrate plus 18 mmol/l NaCl do not prevent mild hypohydration in trained, heat acclimatized girls with high sweating rates. However, there is a tendency towards a greater fluid retention with the CNa beverage.
European Journal of Applied Physiology