Luetkemeier, M. J., & Stofan, J. R. (2009). Effects of electrolytes in drinks ingested before and during cycling time trials. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 2104.

This study determined whether the addition of electrolytes to drinks consumed before and during exercise improved cycling time trial performance. Healthy, active males (N = 7) participated in four randomly ordered conditions combining one of two pre-exercise drink formulations with one of two during-exercise drink formulations. Each condition consisted of a two-hour drinking phase followed immediately by a cycling time trial designed to last ~90 minutes. The two 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 g/L, K = 0.375 g/L). The four conditions Ww, We, Ew, and Ee, which were assessed for time-trial performance, fluid balance and change in relative plasma volume (PV).

Urine rates during the drinking phase were higher for Ww and We than for Ew and Ee leading to a greater positive fluid balance (input - output) for Ew and Ee than Ww and We. Fluid balance differences were largely attributed to disparity in urinary free water clearance in the Ew and Ee (conditions. Change in plasma volume from blood samples taken before and after the drinking phase was greater for Ew and Ee than for Ww and We. This difference in plasma volume was not associated with heart rate, stroke volume, cardiac output, or blood pressure. Cycling time was slower for Ww when compared to times for Ew, We, and Ee which were not different among each other.

Implication. Pre-exercise administration of a drink containing an electrolyte mixture caused a reduction in urine output leading to a higher fluid balance and plasma volume. Cycling time trial performance lasting ~90-min was improved in conditions where electrolytes were added.

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