The Effect of Fluid Replacement on Endurance Performance

The purpose of this study was to examine the effects of fluid replacement on power output (PO), rating of perceived exertion (RPE), heart rate (HR), body weight (BW), urine osmolarity (U_osm), and urine electrolyte concentrations ([U_Na+], [U_K+], [U_Cl-]) in physically active men (n = 4) and women (n = 7). The participants were asked to generate their highest possible PO during 60 minutes of cycling under 3 randomized conditions: ingestion of (a) no fluid (trial 1); (b) 1200 ml of distilled water (trial 2); and (c) 1200 ml of Gatorade (trial 3). BW and urine volume (V_u) were measured before and after the ride to determine sweat rate [(SR = ΔBW + V_{fluid intake} + V_u)/time]. The results indicated that there were no significant differences between trials for PO (123-127 W), RPE (14), HR (140-142 b·min^-1), and SR (11.9-12.4 ml·min^-1). However, [U_Na+] was significantly (p <0.05) lower postexercise for all 3 trials, and [U_Cl-] was significantly reduced following trials 2 and 3. There was a significant increase (p <0.001) in BW postexercise for trials 2 and 3 when compared with the no-fluid trial; however, the effects of water and Gatorade were similar. These results suggest that fluid replacement during 1 hour of moderately intense cycling does not enhance performance in physically active men and women who are normally hydrated.