Effects Of Electrolytes In Drinks Ingested Before And During Cycling Time Trials

Abstract

PURPOSE: To determine whether the addition of electrolytes to drinks consumed before and during exercise improves cycling time trial performance. METHODS: Healthy, active males (n=7; mean age=38.8±5.1 years, weight=75.1± 6.1 kg, %fat=12.7±5.3%, OBLA=215 ±38 Watts) participated in 4 randomly ordered conditions combining 1 of 2 pre-exercise drink formulations with 1 of 2 during-exercise drink formulations. Each condition consisted of a 2-h drinking phase followed immediately by a cycling time trial designed to last ∼90-min. The 2 pre-exercise drinks (13-ml/kg BW) were either (W) flavored water or (E) flavored water containing 9.62 g/L of Gatorlytes electrolyte mixture (Na=2.18 g/L, K=1.10 g/L, Osm=300 mOsm/L). The during-exercise drinks (17-ml/kg BW) were either (w) a 6% carbohydrate beverage or (e) a 6% carbohydrate beverage plus electrolytes (Na =0.83 grams/L, K=0.375g/L). Thus, the 4 conditions were Ww, We, Ew, and Ee, which were tested using 1-way ANOVA for effects on primary outcomes of time-trial performance, fluid balance and change in relative plasma volume (PV). RESULTS: Urine rates during the drinking phase were higher for Ww and We (9.43± 3.15 ml/min) than for Ew and Ee (5.98±ml/min) leading to a greater positive fluid balance (input - output) for Ew and Ee (+199± 280ml) vs. Ww and We (-109±365 ml). Fluid balance differences were largely attributed to disparity in urinary free water clearance between Ew and Ee (0.5±1.8 ml/min) vs. Ww and We (4.2±2.3 ml/min). Change in PV from blood samples taken before and after the drinking phase was greater for Ew and Ee (1.5±10.0 ml) than for Ww and We (-4.6±6.9 ml). This difference in PV was not assoc. with s.d's. in HR, SV, CO or BP. Cycling time was slower (p<0.05) for Ww (90.1± 6.0 min) compared to times for Ew (85.4±6.2 min), We (87.0±5.7 min) and Ee (87.6±6.2 min), which were not different among each other (p>0.05). CONCLUSION: Pre-exercise administration of a drink containing a 300 mOsm/L electrolyte mixture caused a reduction in urine output leading to a higher fluid balance and PV. Cycling time trial performance lasting ∼90-min was improved in conditions where electrolytes were added to the drink either before or during exercise but there was no additional improvement in performance when electrolytes were added to both the before and during-exercise drinks.