Twenty (12 male and 8 female) tennis players from two Division I university tennis teams performed three days of round-robin tournament play (i.e., two singles tennis matches followed by one doubles match per day) in a hot environment (32.2 ± and 53.9 ± 2.4% rh at 1200 hr), so that fluid-electrolyte balance could be evaluated. During singles play, body weight percentage changes were minimal and were similar for males and females (males -1.3 ± 0.8%, females -0.7 ± 0.8%). Estimated daily losses (mmol · ) of sweat sodium (Na+) and potassium (K+) (males, 158.7, 31.3; females, 86.5, 18.9) were met by the players' daily dietary intakes (mmol · ) of these electrolytes (males, 279.1 ± 109.4, 173.5 ± 57.7; females, 178.9 ± 68.9, 116.1 ± 37.5). Daily plasma volume and electrolyte (Na+, ) levels were generally conserved, although, plasma [Na+] was lower (p < .05) on the morning of Day 4. This study indicated that these athletes generally maintained overall fluid-electrolyte balance, in response to playing multiple tennis matches on 3 successive days in a hot environment, without the occurrence of heat illness.
M.F. Bergeron was with the Human Performance Laboratory, University of Connecticut, at the time of this study and is now with the Department of Health Science, College of Health, University of N. Florida, 4567 St. Johns Bluff Rd. South, Jacksonville, FL 32224. C.M. Maresh, L.E. Armstrong, J.W. Castellani, R.W. Kenefick, K.E. LaGasse, and D.A. Riebe are with the Human Performance Laboratory, University of Connecticut, Storrs, CT 06269. J.F. Signorile is with the Human Performance Laboratory, Department of Exercise and Sport Sciences, University of Miami, Coral Gables, FL 33124.