Endocrine Responses Toexercise

Exercise causes a 20- to 25-fold increase in whole body energy metabolism, and oxygen uptake can increase from resting levels of approximately 0.3 1/min and up to 6-7 1/min in highly trained endurance athletes. This results in an increased glycolysis and glycogenolysis in muscle tissue, an increased glycogenolysis and gluconeogenesis in the liver, an increased lipolytic activity in adipose tissue as well as in intramuscular fat depots, and to a minor extent an increased protein breakdown in muscle tissue. These dramatic changes in fuel requirements, together with cardiovascular adjustments needed to accomplish the increased demand for muscle tissue oxygen supply, require a strong regulation in order to maintain internal homeostasis during exercise. Changes in autonomic nervous activity and in hormone secretion are central in this respect; and the present chapter will review the hormonal responses to acute exercise as well as the adaptation to training, in order to provide basis for understanding of a possible coupling of changes in the hormonal system and the immune system during physical activity⁴⁷ (see Chapter 5).