Exercise and the Autonomic Nervous System

Publisher Summary This chapter discusses the roles of the autonomic nervous system (ANS) in the regulation of the cardiovascular response during exercise. At the onset of exercise, the central nervous system (CNS) generates a cardiorespiratory pattern (central command) appropriate to the somatomotor signal. The central command then initiates a withdrawal of parasympathetic activity to the heart and an increase in ventilation rate, and is also probably involved in the resetting of the arterial baroreflex toward greater pressures. Although little is known about the central neural connections involved in initiating the changes in parasympathetic and sympathetic outflows in the exercised state, it is known that central command and the arterial baroreflexes are critical to the sympathoexcitatory response at the onset of exercise. In most animal models and humans, there is redistribution of cardiac output to the exercising muscle; this involves an increase in sympathetic outflow to the visceral organs that results in an increase in vascular resistance in these regions. Conversely, the resistance to the exercising muscle is diminished. The increased resistance to the nonexercising regions is initially the result of the upward resetting of the arterial baroreflex. As the exercise continues, an additional increase in vascular resistance may occur because of the activation of chemosensitive muscle afferents.