Glucose polymer solutions and prolonged exertion in the heat

The effect of glucose polymer solutions on physical performance has been extensively investigated, mainly under controlled laboratory conditions. The influence of such beverages on fluid balance and on glycemic state in the field, during prolonged exercise of moderate intensity (a 134 km march) in the heat (32-41 degrees C, 60-14% relative humidity) was therefore studied. 48 endurance-trained men were randomly assigned to drink either a 7.2% glucose polymer (GP) electrolyte beverage or tap water (TW); there were 24 in each group. Each group was then divided into subgroups that either consumed fluid ad libitum, or were instructed to consume 1000 ml/hr. Mean fluid consumption of all subgroups was similar. There was a greater change in plasma volume for the TW than for the GP group (+7.9% vs. +4.8%, respectively; p less than 0.05). However, in neither the GP nor the TP group did dehydration exceed 2% of body weight. Blood glucose concentration increased significantly in subjects ingesting GP (p less than 0.01) while it decreased on each day of march in those drinking TW. It is concluded that the fluid intake recommended at present by the IDF is adequate to maintain hydration within the normal range during physical effort in the heat. The differences between the GP and the TW groups in this study do not justify the substitution of glucose-polymer solutions for water during prolonged, moderate exercise.