DeMarco, H. M., Sucher, K, P., Cisar, C. J. & Butterfield, G. E. (1999). Pre-exercise carbohydrate meals: Application of glycemic index. Medicine and Science in Sports and Exercise, 31, 164-170.

Oxidation of plasma glucose increases during the latter stages of prolonged strenuous exercise when muscle glycogen nears depletion. Anything that will increase the availability of glucose at that stage should enhance performance.

This study compared postprandial glycemic, insulinemic, and physiologic responses to a pre-exercise meal calculated to have a low glycemic index (LGI - All-Bran, apple, unsweetened yogurt) or a high glycemic index (HGI - cornflakes, banana, milk). Meal size was 1.5 gm/kgBW. Trained cyclists (N = 10) ate the meal with water 30 minutes before cycling for two hours at 70% VO2max, which was then followed by cycling to exhaustion at 100% VO2max.

Plasma insulin levels were significantly lower after the LGI rather than the HGI meal after 20 minutes of exercise. RER was higher after two hours of exercise for the HGI than the LGI group. At that time, RPE was lower and plasma glucose levels higher for the LGI group. Time to exhaustion was 59% longer after the LGI group.

Implication. A low glycemic index pre-exercise meal should extend prolonged performance over that provided by a high glycemic meal. As well, the quality of finishing performance should be improved.

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