Your blood pressure has two components: the systolic pressure, which is the pressure in your blood vessels when your heart contracts, and the diastolic pressure, which is the pressure in your vessels when your heart relaxes. If these numbers are 120 and 80, respectively, your blood pressure would be expressed as "120/80 millimeters of mercury" -- perfectly normal blood pressure.
But what happens to that reading during exercise?
During aerobic exercises (jogging, dancing, swimming or cycling) your heart rate rises, your systolic blood pressure rises and your diastolic pressure either remains the same or rises slightly. These effects are primarily caused by stimulating chemicals, such as adrenalin, produced by your sympathetic nervous system.
Yet aerobic exercise activates the sympathetic nervous system much less if you work out regularly; your blood vessels will be more relaxed and will impose less resistance against blood flow. As a result, your blood pressure at rest will be lower. That's why aerobic exercise is often prescribed to help treat mildly elevated blood pressure.
During static exercise (weightlifting or isometric exercises), your heart rate, systolic blood pressure and diastolic blood pressure all increase. This type of exercise may be dangerous for people who have heart disease because the increased pressure could cause a damaged heart to beat irregularly or could cause a blood vessel to burst anywhere in the body.
Q: Is it OK to take a cold shower after I work out? My aerobics instructor says it could make me pass out. Why?
A: Many people find cold showers invigorating after a tough workout. They're perfectly safe for most people. However, people with high blood pressure or certain forms of heart disease should avoid cold showers.
During exercise, your internal body temperature rises. The blood vessels in your skin then widen to help release some of the built-up heat. But the opposite occurs when your internal body temperature starts to fall. Cold temperatures narrow the blood vessels in your skin so more blood remains internally, keeping your vital organs warm. Whenever the blood vessels in your skin narrow, your blood pressure rises. This reaction can be dangerous for people with heart disease.
But if you have a healthy heart, go ahead and cool off in the shower!
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.