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Effect of Time and Diet Since Last Exercise Bout on Glycogen Stores

Immediately after the exercise bout is completed, the glucose produced by the liver is used to ensure that the blood glucose level is returned to normal, and then it is used to restock the glycogen stores first of the heart and then of the skeletal muscles (Gaesser & Brooks, 1980). Only when all these stores are replete do the liver glycogen stores begin to be filled.

This resynthesis is aided by a high-carbohydrate diet. Trained athletes who eat high-carbohydrate diets can probably restock their entire carbohydrate stores within 24 hours of moderate exercise (Brouns, 1988; Costill & Miller, 1980). The rate of muscle glycogen resynthesis after a standard marathon race (see Exercises 3.3) is somewhat slower (W.M. Sherman et al, 1983), probably because racing-induced muscle damage slows the normally high rate of glycogen resynthesis in trained subjects.

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The classic studies of the effects of exercise and dietary manipulation on muscle glycogen levels were performed in 1967 by Scandinavian groups led by Jonas Bergstrom (Bergstrom et al, 1967a; Bergstrom & Hultman, 1967a, 1967b) and Bjom Ahlborg (B. Ahlborg et al, 1967a, 1967b). These studies led directly to the widespread use by marathon runners in the 1970s of the prerace “carbohydrate-depletion/carbohydrate-loading” diet. is a synthesis of the findings of B. Ahlborg et al. (1967a).

B. Ahlborg and his colleagues took three groups of Scandinavian army conscripts (Groups A, B, and C) and exposed them to the following experimental regime.

Group A subjects performed exercise to exhaustion on Day -3 and then ate high-fat, high-protein, low-carbohydrate diets for the next 3 days. On Day 0 they again exercised to exhaustion, and for the next 7 days (Days 1 through 7) they ate high-carbohydrate (90%) diets.

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