Carbohydrate feeding during prolonged strenuous exercise can delay fatigue

This study was undertaken to determine whether carbohydrate feeding during exercise can delay the development of fatigue. Ten trained cyclists performed two bicycle ergometer exercise tests 1 wk apart. The initial work rate required 74 ± 2% of maximum O₂ consumption (V̇O₂(max)) (range 70-79% of V̇O₂(max)). The point of fatigue was defined as the time at which the exercise intensity the subjects could maintain decreased below their initial work rate by 10% of V̇O₂(max). During one exercise test the subjects were fed a glucose polymer solution beginning 20 min after the onset of exercise; during the other they were given a placebo. Blood glucose concentration was 20-40% higher during the exercise after carbohydrate ingestion than during the exercise without carbohydrate feeding. The exercise-induced decrease in plasma insulin was prevented by carbohydrate feeding. The respiratory exchange ratio was unchanged by the glucose feeding. Fatigue was postponed by carbohydrate feeding in 7 of the 10 subjects. This effect appeared to be mediated by prevention of hypoglycemia in only 2 subjects. The exercise time to fatigue for the 10 subjects averaged 134 ± 6 min (mean ± SE) without and 157 ± 5 min with carbohydrate feeding (P < 0.01).