Significance of skeletal muscle oxidative enzyme enhancement with endurance training

A theoretical model is proposed to explain how the increase in mitochondrial protein concentration, and therefore of the oxidative enzymes, that occurs with endurance training could operate to alter the choice of substrate during submaximal exercise in a manner such that the oxidation of fatty acids increases, glycogen depletion and lactate production are reduced, and work capacity is enhanced. The model is based on the control of enzyme activities both by enzyme and substrate concentrations. The effect of altering enzyme concentration on reaction velocities is presented on the basis of standard Henri-Michaelis-Menten kinetics. It is shown that the reaction velocity at a given substrate concentration is a function of total enzyme concentration. With an increase in total enzyme concentration there is a parallel increase in reaction velocity at the same substrate level. This would have its greatest impact at substrate levels below the Km of the enzyme. It would have an effect of enhancing fatty acid flux through the oxidative pathways while inhibiting the Embden-Meyerhof pathway. The model, as proposed, is consistent with known alterations in metabolism as they occur in man during submaximal exercise following endurance training.