Metabolic control principles and 31P NMR

31P NMR is a unique research tool for studying metabolism during exercise. This communication gives the underlying theory and experimental data for obtaining the transfer characteristic relating work and NMR-determined metabolic paramenters, particularly the ratio of free inorganic phosphate to phosphocreatine (Pi/PCr). Furthermore, illustrations of the types of transfer characteristics observed in different individuals and different training regimens can be obtained, including both hyperbolic (Michaelis-Menten) and sigmoid transfer characteristics. With a hyperbolic transfer characteristic, oxygen delivery appears to be adequate to support the exercise regimen over the range studied (up to 50% of Vmax), whereas with a sigmoid transfer characteristic, there appears an imprint of limited oxygen delivery on the kinetics from rest up to 50% of Vmax. These two types of transfer functions are appropriate to explain the transition to anaerobic metabolism (anaerobic threshold), with a hyperbolic transfer characteristic representing a graded transition; and a sigmoid transfer characteristic representing an abrupt transition. A sigmoid transfer characteristic may involve greater lactate accumulation at submaximal exercise levels, and in both types of transfer characteristic sufficient aerobic lactate is formed to meet the metabolic demand for pyruvate. The results suggest an important role for 31 P NMR in studies of energy-related metabolites as a means of determining exercise performance in terms of regulation of tissue oxidative metabolism and oxygen delivery to tissue.