Chapter 27 Summary 32 Exercise 1. In anticipation of exercise the vagus nerve impulses to the heart are inhibited and the sympathetic nervous system is activated by central command. The result is an increase in heart rate, myocardial contractile force, and regional vascular resistance. With exercise, vascular resistance increases in skin, kidneys, splanchnic regions, and inactive muscles and decreases in active muscles. The increase in cardiac output is mainly caused by the increase in heart rate.
Stroke volume increases only slightly.
Total peripheral resistance decreases, oxygen consumption and blood oxygen extraction increase, and systolic and mean blood pressure increase slightly. As body temperature rises during exercise, the skin blood vessels dilate. However, when heart rate becomes maximal during severe exercise, the skin vessels constrict. This increases the effective blood volume but causes greater increases in body temperature and a feeling of exhaustion. The limiting factor in exercise performance is the delivery of blood to the active muscles.