Fluid-electrolyte balance associated with tennis match play in a hot environment

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 ± 1.5°C 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 · day^-1) of sweat sodium (Na⁺) and potassium (K⁺) (males, Na⁺ 158.7, K⁺ 31.3: females, Na⁺ 86.5, K⁺ 18.9) were met by the players' daily dietary intakes (mmol · day^-1) of these electrolytes (males, Na⁺ 279.1 ± 109.4, K⁺ 173.5 ± 57.7; females, Na⁺ 178.9 ± 68.9, K⁺ 116.1 ± 37.5). Daily plasma volume and electrolyte (Na⁺, K⁺) levels were genera1ly 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.