The Effect of Fluid and Carbohydrate Feedings During Intermittent Cycling Exercise

The purpose of this study was to determine the effect of ingesting water or carbohydrates solutions on physiologic function and performance during 1.6 h of intermittent cycling exercise in the heat (dry bulb temperature = 33 degrees C). Thirteen male subjects (24 to 35 yr) completed four separate rides. Each ride consisted of intermittent steady-state cycling (at 55 and 65% VO2max) interspersed with five rest periods. A timed 480 revolution cycling task completed each experimental session. During each rest period, subjects consumed 2 ml.kg-1 body weight of water placebo or solutions of 5% glucose polymer, 6% sucrose/glucose, or 7% glucose polymer/fructose. Beverages were administered in double-blind, counter-balanced order. No differences were observed among subjects in response to beverage treatments for changes in plasma concentrations of total proteins, sodium, potassium, lactate, or in osmolality, percent change in plasma volume, heart rate, oxygen uptake, respiratory exchange ratio, rating of perceived exertion, sweat rate, rectal temperature, or mean skin temperature. Compared to water placebo, the carbohydrate treatments produced higher plasma glucose values following 1 h cycling (P less than 0.01). Mean (SD) times for the 480 revolution cycling task: water placebo = 432 (43) s; glucose polymer = 401 (52) s; *sucrose/glucose = 384 (39) s; and *glucose polymer/fructose = 375 (30) s, where = P less than 0.001 compared to water placebo. Physiologic function was similarly maintained during exercise by all beverage treatments, while ingestion of sucrose/glucose and glucose polymer/fructose resulted in improved end-exercise cycling performance.