studies have confirmed that aerobic endurance is directly related to the body's carbohydrate supply and that carbohydrate supplementation can enhance endurance performance. The purposes of this paper are to review the latest information on the effectiveness of carbohydrate supplements to improve aerobic endurance and to review the most effective means of rapidly replenishing the body's carbohydrate stores after exercise.
Christensen and Hansen (1939a,b) reported that a high-carbohydrate diet could delay the onset of hypoglycemia and increase the time to exhaustion during prolonged exercise and that a carbohydrate supplement ingested at the time of exhaustion could rapidly alleviate hypoglycemia and substantially prolong the exercise period. Bagby et al. (1978) demonstrated that continuous infusion of rats with glucose during moderate-intensity running reduced the rate of liver and muscle glycogen utilization and delayed the onset of fatigue. The use of carbohydrate food supplements intermittently during exercise has also been shown to improve endurance performance (Coyle et al., 1983, 1986; Fielding et al., 1985; Hargreaves et al., 1984; Ivy et al., 1979, 1983). To study this effect, we encouraged cyclists to maximize work output during 2 h of isokinetic cycling (Ivy et al., 1979). The subjects were fed either a placebo or 0.2 g of glucose polymer per kilogram of body weight every 15 min during the first 90 min of exercise. There was no improvement in total work accomplished between the placebo and glucose polymer trials. However, during the last 30 min of exercise, the work production for the glucose polymer trial exceeded that of the placebo trial by 11% (Figure 5-1). Of even greater interest was the finding that during the last 10 minutes of the glucose polymer trial, work production was increased to a level in excess of that found over the first 10 min of exercise. These findings were interpreted as indicating that glucose feedings may be of benefit during prolonged exercise lasting longer than 90 min (Ivy et al., 1979).
To investigate this possibility, we had subjects walk to exhaustion while consuming a carbohydrate supplement or placebo (Ivy et al., 1983). Subjects walked on a motorized treadmill with the speed and incline set to elicit an exercise intensity of 45% maximal O2 uptake . The carbohydrate