Effects Of Coconut Water, Electrolyte Water, And Water On Endurance Running Performance In The Heat

Abstract

Coconut water (CW) is often referred to as "nature's sports drink" because of its high electrolyte (primarily potassium) content. However, the efficacy of CW in maintaining hydration or performance during exercise has not been investigated. PURPOSE: To compare the effects of CW (Amacoco; 5.6% carbohydrate, 48 mM K, 6 mM Na, 4 mM Ca, 3 mM Mg, 37 mM Cl), electrolyte water (EW; 45 mM K, 8 mM Na, 5 mM Ca, 3 mM Mg, 37 mM Cl), and water placebo (P) on performance. METHODS: Seventeen endurance-trained men (21-45 y) completed a 90-min steady state run (preload, 65% VO2max) followed by a 10K time trial in a warm environment (28°C). During preload, subjects drank a volume of CW, EW, or P (randomized, double-blind) to replace 80% of sweat losses. Venous blood samples were taken at baseline and at 30-min intervals during the 2-h preload run. [Hct] and [Hb] were measured in whole blood to determine percent change in plasma volume. Blood serum was analyzed for osmolality and electrolyte concentrations. Nude body weight was measured before and after exercise to assess fluid balance. RESULTS: There were no differences in 10K finish times among trials (2621 ± 383, 2629 ± 408, and 2622 ± 373 sec in CW, EW, and P trials respectively). In addition, the change in plasma volume (-9.6 ± 8.1, -9.3 ± 5.4, and -9.6 ± 5.2% in CW, EW, and P trials respectively) and change in body mass (-0.6 ± 0.4, -0.6 ± 0.5, and -0.5 ± 0.4% in CW, EW, and P trials respectively) were not different among trials. Post-preload serum osmolality (293 ± 6 vs. 299 ± 4 and 297 ± 6 mOsmol/kg), [K] (5.1 ± 0.4 vs. 5.9 ± 0.5 and 5.8 ± 0.4 mM), [Cl] (98 ± 2 vs. 100 ± 2 and 100 ± 2 mM), and [Mg] (1.86 ± 0.13 vs. 2.05 ± 0.12 and 1.95 ± 0.16 mg/dl) were significantly lower in the P vs. CW and EW trials. In addition, post-preload serum [Ca] was lower in P (9.7 ± 0.4) vs. CW (10.0 ± 0.4) and serum [Na] was lower in P (143 ± 3) and EW (143 ± 2) compared with CW (145 ± 3). (All values are means ± SD). CONCLUSIONS: Coconut water is not superior to water for maintaining performance in endurance-trained runners.