Muscle Glycogen during Prolonged Severe Exercise

Abstract 10 well trained and 10 untrained subjects worked to complete exhaustion on a bicycle ergometer with work loads averaging 77 (76–87) per cent of their individual maximal aerobic power. Determinations of glycogen used by working muscles (biopsy of lateral portion of the quadriceps femoris muscles) and of combusted carbohydrate (V o2 and RQ) were performed at certain intervals from the start of work to exhaustion. At a combustion rate of about 3 g carbohydrate per minute (RQ around 0.9 or higher) and at average values for glycogen in resting muscle of 1.6 (1.1–2.5)g/100 wet muscle, the effective work time was around 85 min for the untrained and 90 min for the trained subjects. At the end of the exhaustive exercise the glycogen content averaged 0.06 g in the untrained and 0.12 g/100 g wet muscle in the trained subjects. A close relationship between utilized glycogen and combusted carbohydrate was found, and it seems highly probable that at high relative workloads primarily the glycogen stores in the exercising muscles will limit the capacity for prolonged strenuous work.