Endurance Exercise: Normal Physiology and Limitations Imposed by Pathological Processes (Part 2).

In brief: Endurance exercise causes rapid changes in physiological and metabolic functions, involving not only the body's oxygen transport system (discussed in part 1 of this article, August 1986, page 94) but also the fuel supply and endocrine systems. The hormonal changes increase glucose delivery by stimulating glycogenolysis and gluconeogenesis in the liver and glycogen utilization in muscles, and also increase free fatty acid delivery by stimulating lipolysis in fat cells. Patients with disorders of muscle energy metabolism may have difficulty performing either brief, intense exercise or prolonged exercise, depending on the disorder. Diseases that cause abnormal hormonal and autonomic responses to exercise include autonomic neuropathy, central Cushing's disease, and diabetes mellitus.