Widzer, M. O., Boon, N., Lichtenberg, L. C. & Ivy, J. L. (2003). Effects of carbohydrate supplementation of pervious exercise and recovery on fuel utilization of subsequent exercise. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 1661.

Several sports have demanding exercise twice daily. Swimming and track have heats in the morning and further competitions in the afternoon or evening. Many sports require twice daily training. This investigation assessed one factor that might pre-dispose athletes to perform better in the second exercise session of the day.

Trained male cyclists (N = 8) completed two exercise trials each with different fluid supplementation. Exercise consisted of 90 minutes of cycling on an ergometer at sub-lactate threshold followed by two hours of recovery. Ss received carbohydrate (8%) or placebo fluid supplementation during the first exercise and recovery. A second 75-minute exercise at the same intensity as in the first was then performed. Immediately following the second exercise, a time-trial was completed.

During the first exercise and recovery, plasma insulin levels were higher during the carbohydrate condition. In the second exercise, insulin and IL-6 levels were similar between treatments, but plasma fatty free acids, glycerol, cortisol, and growth hormone levels were suppressed during the carbohydrate condition. This indicated a lower fat and higher carbohydrate oxidation rate during the carbohydrate condition. There was no difference in time trial performances despite different substrate utilizations.

Implication. Carbohydrate supplementation during and after an early exercise session will not improve performance in a second session on the same day.

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