Beta blockers: How do they affect target heart rate?

If you're taking beta blockers, you shouldn't use target heart rate to judge the intensity of your workout. Beta blockers cause your heart to beat more slowly. This can prevent the increase in heart rate that typically occurs with exercise. As a result, the usual age-adjusted target heart rate doesn't work — because no matter how vigorously you exercise you may never achieve your "target."

There's no precise method for predicting the effect of beta blockers on your heart rate. An exercise stress test can evaluate your exercise capacity on beta blockers and provide an adjusted target heart rate.

If you haven't had an exercise stress test, you can use the perceived exertion scale, which relies on your own judgment of how hard you're working based on effort, breathlessness and fatigue. The scale ranges from 6 (at rest) to 20 (maximal effort). For most workouts, your best bet is to aim for moderate intensity, or a rating between 12 and 14.