Older studies seem to suggest a correlation between free fatty acid (FFA) turnover and
oxidation on the one hand and plasma
FFA concentration on the other during
submaximal exercise. However, recent studies, in which higher concentrations of plasma FFA have been reached during prolonged submaximal exercise, have revealed a leveling-off in net uptake in spite of increasing plasma FFA concentrations. Furthermore, endurance training alters this relationship between FFA concentration and FFA uptake and
oxidation. These recent findings in humans support the notion from other cell types that trans-membrane fatty acid transport is not only by simple diffusion, but also predominantly carrier-mediated.
During prolonged submaximal knee-extension exercise it has been demonstrated that the total oxidation of fatty acids was approximately 60% higher in trained subjects than untrained subjects. The training-induced adaptations responsible for this increased utilization of plasma fatty acids by muscle could be located at several steps ranging from the mobilization of fatty acids to skeletal muscle metabolism in the mitochondria.
Implication. As a response to training, the body increases its ability to use fatty acids as fuel before calling on glycogen for energy.