Muscle Glycogen Utilization During Work of Different Intensities

Abstract

The relative contributions of different substrates for the energy metabolism during exercise have been discussed repeatedly during the last 100 years. The greater importance for carbohydrates at heavy work intensities, which the increase in respiratory exchange ratio (RQ) implies (4), has received strong support from studies in which the glycogen breakdown in exercising muscles has been determined (7,8,13). The factors determining muscle glycogen utilization during heavy muscular work are not well understood. In this article results will be presented on glycogen utilization at different work intensities. Further, the possibility of changing the rate of glycogen utilization at a given absolute or relative work load has been investigated in conditions of lowered barometric pressure and after physical conditioning. On the basis of these results and evidence from animal experiments, it is suggested that the main determinant for the metabolic response observed during exercise in man is related to the recruitment pattern for motor units in the muscles.