My Heart Knows When to Beat Faster: : How the Human Body Anticipates its own Needs During Exercise

Exercise places a series of competing demands on the human body. First, as muscles work harder, they require a larger blood supply. This entails a whole-body shift: Blood vessels in the periphery widen to accommodate more volume, and blood vessels in the gut contract, forcing even more blood out to the muscles. To keep this volume circulating, the heart pumps faster and ejects more volume on each stroke. To maintain the supply of oxygen and remove carbon dioxide, the rate and depth of breathing also increase. The sympathetic branch of the autonomic nervous system plays a significant role in all these changes that allow us to exercise. But how does the autonomic nervous system know that the body is exercising? What signal tells this system to execute such significant changes? Perhaps it is our conscious perception of the fact that we are exercising, or perhaps some receptor in our muscles tells the autonomic nervous system that the muscles are active and need more blood. In fact it is a combination of these concepts. Three systems, known as central command, the baroreflex, and the exercise pressor reflex, mediate the autonomic response to exercise