Human Skeletal Muscle Glycogen Branching Enzyme Activities with Exercise and Training

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Abstract
Sixteen healthy male subjects classified as sedentary (8) or active (8), exercised to exhaustion on a bicycle ergometer at a load requiring 70% of their maximal aerobic capacity. Biopsy samples of the vastus lateralis muscle were taken at rest and at the time of fatigue. A 12 week training program increased skeletal muscle glycogen content and branching enzyme activities twofold. The exhaustive submaximal exercise reduced the glycogen levels of the trained group to values similar to the fatigue levels of the non-trained subjects. Skeletal muscle glycogen branching enzyme activities decreased with submaximal exercise to fatigue in all groups. Maximal exercise to fatigue resulted in small increases in the activities of the enzyme. The results of the present study and a previous study (Taylor et al. 1972. Can. J. Physiol. Pharmacol. 50, 411–415) indicate that the activities of the glycogen synthesizing enzymes are highly correlated with the skeletal muscle resting glycogen concentration and the relative fitness of the subjects.

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