Fluid replacement drinks during high intensity exercise effects on minimizing exercise-induced disturbances in homeostasis

Summary The purpose of these experiments was to examine the influence of various fluid replacement drinks on exercise-induced disturbances in homeostasis during heavy exercise. Nine trained cyclists performed constant load exercise on a cycle ergometer to fatigue on three occasions with 1-week separating experiments. The work rate was set initially at 85% of (range 82–88%) with fatigue being defined as a 10% decline in power output below the initial value. During each experiment subjects consumed one of the following three beverages prior to and every 15 min during exercise: (1) non-electrolyte placebo (NEP; 31 mosmol · kg^–1); (2) glucose polymer drink containing electrolytes (GP; 7% CHO, 231 mosmol · kg^–1), and (3) electrolyte placebo drink without carbohydrate (EP; 48 mosmol · kg^–1). Both the GP and EP beverage contained sodium citrate/citric acid (C) as a flavoring agent while C was not contained in the NEP drink. Although seven of nine subjects worked longer during the GP and EP treatment when compared with the NEP trial, the difference was not significant (P>0.05). No differences (P>0.05) existed between the GP and EP treatments in performance time. Exercise changes in rectal temperature, heart rate, % plasma volume and plasma concentrations of total protein, free fatty acids, glucose, lactate, potassium, chloride, calcium, and sodium did not differ (P>0.05) between trials. In contrast, blood hydrogen ion concentration [H⁺] was significantly lower (P<0.05) at 30 min of exercise during the GP and EP treatment when compared with the NEP run. These data provide evidence that electrolyte drinks do not minimize exercise-induced disturbances in blood-electrolyte concentrations during heavy execrcise when compared with nonelectrolyte drinks; however, these results suggest that fluid replacement beverages containing buffers (i.e. C) and/or electrolytes may minimize blood alterations in [H⁺] during intense exercise. Additional research is required to determine if the buffering influence of these beverages has an ergogenic benefit during heavy exercise.