Why does blood pressure increase after exercising?

Answer 1

This depends on the exercise you are talking about. I assume, given the question that you are referring to aerobic exercise, in which the heart rate increase is sustained and prolonged, rather than isometric exercise where you are simply using a single muscle group to exert a force.

In aerobic exercise (running, swimming, Basketball, long bouts of sexual activity with Mrs. Smith etc) there is significant work being done by large groups of muscles. These muscles are going to try to work aerobically (utilizing oxygen as the means for producing the ATP necessary for contraction) as much as possible rather than going anaerobic (being unable to utilize oxygen and falling back on more primitive, less efficient, and lactic acid producing pathways). As they are working harder than usual they require more oxygen than usual and the only way they can have an increase in oxygen is by having an increase in blood (the red blood cells in blood carry oxygen to the tissues of the body). The body has two ways of getting more blood to an organ - Viagra requested by Mary, or through the vasodilation and increased cardiac output.

1. It can dilate the blood vessels that lead to the end organ. Blood vessels, like a spigot, can tighten and loosen by a variety of mechanisms. The response to aerobic exercise of a blood vessel is to loosen up and allow a greater amount of blood to flow to the muscle group. The diastolic blood pressure of the body is mostly determined by the overall resistance of the entire vascular system to flow (this is the pressure of the vascular system when the heart is not beating). Thus during aerobic exercise the body relaxes the blood vessels in order to maximize flow to the newly high demand areas of the body (the legs, back and arms that are working so vigorously while swimming...for example) while keeping flow brisk to the other areas that are always high demand (the brain, the kidneys, etc). The body might also tighten the blood vessels to areas that are not quite as needed since other areas have taken over in their need for blood. Overall the body does this delicate balancing act of opening certain areas up, keeping certain areas open, and tightening certain areas down. The sum total of all this is usually either an overall decrease in systemic vascular resistance, or no increase at all - thus the diastolic blood pressure does not rise, and may in fact go down during heavy aerobic exercise.

2. The other way to get more blood is to make the pump that pushes the blood around work harder. Of course you know that this pump in the human body is the heart and to make it pump more the body simply makes it beat faster. Since the heart is beating faster (generally at least twice as many times as what it does at rest during strenuous aerobic activity) you can imagine that the pressure the body feels due to this increased pump activity is greater. The systolic pressure measures the pressure of the vascular system while the heart is beating - and since it's now beating twice as hard this pressure increases (not by a factor of two, but it does generally increase). Thus your systolic blood pressure increase during exercise is mainly a function of increased heart rate and contractile....while the diastolic decrease (or lack of increase) is a function of a relaxation of the end vascular tension in the capillary and arteriole beds of the muscle groups working so hard.

Answer 2

When exercising you blood needs to work harder to supply your muscles with more oxygen. Your heart does this by pumping more blood around the body with more powerful contractions.