FLUID BALANCE OF ADOLESCENT SWIMMERS DURING TRAINING J. D. ADAMS, 1 STAVROS A. KAVOURAS, 1 JOSEPH I. ROBILLARD, 1 COSTAS N. BARDIS, 1 EVAN C. JOHNSON, 1 MATTHEW S. GANIO, 1 BRENDON P. MCDERMOTT, 1 AND MICHAEL A. WHITE 2 1 Department of Health, Human Performance, and Recreation, Human Performance Laboratory, University of Arkansas, Fayetteville, Arkansas; and 2 Sun Prairie Storm Swim Club, Racine, Wisconsin ABSTRACT Adams, JD, Kavouras, SA, Robillard, JI, Bardis, CN, Johnson, EC, Ganio, MS, McDermott, BP, and White, MA. Fluid balance of adolescent swimmers during training. J Strength Cond Res 30(3): 621–625, 2016—Swimming, either competitively or leisurely, is a unique activity that involves prolonged exercise while immersed in stable water temperatures. This environment could have an influence on the hydration status of swimmers independently of fluid balance. Forty-six healthy adolescent swimmers (26 males and 20 females; 12.8 6 2.3 years; 50.6 6 13.4 kg) were studied during a typical training session in an indoor swimming pool. First morning, prepractice and postpractice urine samples were tested for osmolality and specific gravity, whereas all athletes consumed fluids ad libitum. Sixty-seven percent of the athletes were hypohydrated (urine osmolality [U osm ] $700 mmol$kg 21 ) based on their first morning urine sample, which increased to 78% immediately before training. During the 2- hour swimming practice, the minimal sweat loss (0.39 6 0.27 L) combined with ad libitum fluid availability resulted in unchanged body weight (0.1 6 0.3 kg). Additionally, thirst was similar (before practice: 46 6 26, after practice: 55 6 33 mm on a 100-mm visual analog scale) at pretraining and posttraining time points (p . 0.05). Interestingly, postpractice U osm was reduced significantly compared with the prepractice value (630 vs. 828 mmol$kg 21 ; p = 0.001), without any significant change in body weight (0.1 6 0.3 kg; p . 0.05). In conclusion, the present data indicated that more than two-thirds of the young swimmers appeared in their practice suboptimally hydrated. Although no changes in body mass were observed during the swimming prac- tice, the decrease in urine hydration markers after swimming might less accurately reflect hydration state. KEY WORDS hypohydration, urine specific gravity, urine osmolality INTRODUCTION M aintenance of fluid homeostasis is vital for ath- letic performance and thermoregulation in youths and adults. Both adults and children fail to drink adequately to replace water loss under warm conditions and exhibit hypohydration even when fluids are provided ad libitum, a phenomenon described as involuntary dehydration (13,28,39). Previous research has shown that adolescent athletes arrive to prac- tice hypohydrated and remain hypohydrated throughout their practice (18). Furthermore, it has been shown that these adolescent athletes remain hypohydrated throughout the training day, until their next practice session (40). During prolonged exercise, dehydration greater than .2% of body mass has been shown to degrade aerobic exercise performance, especially in hot weather (20). The greater the dehydration level, the greater the physiological strain and performance decrement (3,31). However, recent research has proposed that during endurance exercise ad libitum drink- ing might be an effective way to address fluid needs during exercise (24,25,38). To our knowledge, there have been few studies investigating the effect of ad libitum drinking on main- tenance of hydration status in adolescents during training (2,15,39). It is important to review this practice with reference to adolescent swimmers to evaluate the best practice for fluid replacement before, during, and after swim training. Aquatic sports are unique in reference to maintenance of hydration status because they combine the stressors associated with exercise and the additional impact of water immersion. During prolonged exercise, urine excretion is reduced, primar- ily because of increased antidiuretic hormone (ADH) and aldosterone (4,6,7,9,36,37). Conversely, during head out water immersion, there is a suppression of ADH secretion and reduced perception of thirst. The hydrostatic pressure exerted by water on the human body expands plasma volume and suppresses peripheral blood pooling, which results in central hypervolemia and central baroreceptor loading (4,27). This cephalic shift in blood volume can suppress both ADH secre- tion and thirst, while increasing the output of dilute urine because of baroreceptor activation (11,12,30). Swimming, either competitively or leisurely, is a unique activity that involves prolonged exercise during water Address correspondence to Stavros A. Kavouras, kavouras@uark.edu. 30(3)/621–625 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association VOLUME 30 | NUMBER 3 | MARCH 2016 | 621 Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.