The Effect of Training on Skeletal Muscle and Exercise Metabolism

This chapter reviews the molecular and metabolic responses in human skeletal muscle to exercise training. Acute changes in various stimuli that trigger adaptations largely depend on the type of exercise performed and particularly the intensity and duration of discrete sessions. These stimuli are linked to the activation and/or repression of an array of intracellular signal transduction pathways, pre- and posttranscriptional processes, and the regulation of protein translation. Given the considerable overlap in these underlying molecular processes, the mechanistic basis for how repeated, acute changes are translated into specific training responses remains a topic of much investigation. Endurance training is primarily associated with an enhanced capacity for oxidative energy provision and a shift in substrate utilization, from carbohydrate to lipid, at a given absolute exercise intensity. Strength training mainly results in increased muscle size, force-generating capacity, and enhanced capacity for non-oxidative energy provision. Sprint training also increases the capacity for non-oxidative energy provision, but can elicit a range of responses, including some that resemble endurance or strength training. Training generally enhances fatigue resistance and performance in a manner that is specific, but not exclusive, to the type of exercise performed. These improvements are owed, in part to training-induced changes in both the maximal capacity for, and the specific utilization of, various substrates during exercise.