A Study of the Glycogen Metabolism during Exercise in Man

The glycogen content of the quadriceps femoris muscle was determined in needle biopsy specimens taken from normal subjects in connexion with muscular work.Work was performed both in the fasting state and during intravenous infusion of glucose. The carbohydrate metabolism of the liver was also studied before and during periods of exercise.The following inferences can be drawn from the results:1. During work, the muscle glycogen falls successively to values approaching zero, and the working capacity decreases when the glycogen store is depleted.2. The glycogen concentration in resting muscle remains unchanged when other muscle groups in the same subject have been emptied of glycogen by exercise.3. If glucose is infused continuously during muscular work, the glycogen consumption is significantly lower than when no glucose is administered. The difference is nevertheless small, and the consumption of muscle glycogen is responsible for the greater part of the energy production, even when the blood sugar level is high.4. The glucose production by the liver increases towards the end of continuous muscular work, but is of relatively small magnitude in comparison to the total carbohydrate metabolism.