How Beta Blockers Affect Your Target Heart Rate

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If you have high blood pressure, treatment often requires medication with a beta blocker, a common type of blood pressure medication that lowers your resting heart rate. Exercising regularly, another important component of managing high blood pressure also lowers your resting heart rate. Hence, if you take a beta blocker, you will need to make some adjustments when calculating your target heart rate while doing aerobic exercise.

How Beta Blockers Lower Blood Pressure

Beta blockers work by blocking the effect of epinephrine (adrenaline) on the tissues—specifically, by blocking the “beta receptors” that bind epinephrine. Among other things, blocking the beta receptors slows the heart rate, reduces the force of contraction of the heart muscle, reduces the amount of oxygen the heart muscle needs to do its work, reduces stress on the vascular system, and tends to lower the blood pressure.

Beta blockers can slow down your heart rate to anywhere between 2 percent to 25 percent of your untreated resting heart rate.

How Exercise Reduces Your Resting Heart Rate

When you do aerobic exercise, blood flow is directed toward the muscles you're using and away from areas that aren't doing much (such as your arms during running, or the digestive tract). There is increased blood flow as well as an increase in the volume of blood returning to the heart. Over time, the left ventricle adapts and enlarges to accommodate the increased volume. This larger cavity can hold more blood, and ejects more blood per beat, even at rest; your resting heart rate drops because each beat delivers a bigger burst of blood, and fewer beats are needed.

Calculating Your Target Heart Rate

Your maximum heart rate—the upper limit of what your cardiovascular system can handle during physical activity—is determined by subtracting your age from 220. So, if you're 35 years old, your maximum heart rate is around 185 beats per minute (bpm).

It is recommended that you exercise within 55 percent to 85 percent of your maximum heart rate for at least 20 to 30 minutes to get the best results from aerobic exercise.

To use your resting heart rate as your guide, figure out the decrease in your heart rate as a result of the beta blocker. For example, if your resting heart rate is 70 bpm without a beta blocker and 50 bpm with a beta blocker, that’s a difference of 20. When calculating your target heart rate, subtract this number from the result. That’s your “beta blocked” target heart rate and is equivalent to what your target heart rate would be without the beta blocker.

To determine your resting heart rate, and monitor it during exercise, you can use a heart rate monitor or simply take your pulse on the inside of your wrist by counting the number of beats per minute.

Brand names for beta-blockers include include Inderal (propranolol), Lopressor (metoprolol),Tenormin (atenolol), and Sectral (acebutolol).

Adjusting Your Exercise Goals

Adjusting your exercise goals based on this change in heart rate is fairly straightforward. If you’ve had an exercise stress test while on beta blockers, the results will provide hard numbers describing your actual exercise capacity. These numbers should be your guide when planning your exercise goals.

If you haven’t had a stress test, you can still approximate your targets using either your resting heart rate or perceived activity as a guide.

Using a System of Perceived Activity

If you prefer, you can also use a system of perceived activity to help determine your target exercise level. This system essentially works by having you rate, on a scale from six (resting) to 20 (maximum effort), how tired you feel during a given activity. If you’re exercising, how difficult does it feel? The more tired you feel, the higher the rating. It will take some experimenting to develop your personal rating scale. Once you have a rough scale in place, your target range corresponds to a rating of about 12 to 14.

A Word From Verywell

If you’re new to exercise, remember to check with your doctor prior to beginning an exercise program to make sure your heart can keep up with what you have planned. He or she may have some suggestions to help you ease into a new exercise program safely.

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