But what about people like me who take drugs such as metoprolol, which lowers the heart rate? Should I adjust my target heart rate for exercise?
Metoprolol (Lopressor, Toprol) belongs to a class of drugs known as beta blockers. As you mentioned, these drugs reduce your heart rate; they also lower blood pressure.
They work by blocking the effects of the hormone epinephrine (also known as adrenaline), causing your heart to beat more slowly and with less force.
These drugs are often prescribed for people who have had a heart attack, as well as those with heart failure, atrial fibrillation, or angina.
To estimate your target heart rate, subtract your age from 220, then multiply that number by 0.8. If you are 70 years old, for instance, your adjusted target heart rate would be (220 – 70) 0.8 = 120 beats per minute.
For people on a beta blocker, one suggestion is to adjust your target heart rate by the same amount that the beta blocker has reduced your resting heart rate (usually around 10 beats per minute).
However, beta blockers may also blunt the rise in heart rate that normally occurs with exercise, so this calculation may not fully capture the limits that the beta blocker puts on your heart.
In fact, that is one of the ways beta blockers are believed to prevent heart attacks — by keeping the heart rate from getting too high.
A simpler strategy is to exercise at a level that feels challenging but not too intense.
Even though your heart rate may not be a good indicator of how hard you’re exercising, you’ll still breathe harder and your muscles will become tired.
Exercise experts often suggest using the “rate of perceived exertion” scale. It ranges from 1 to 10, with 1 being very easy exercise that has little effect on breathing and 10 indicating very vigorous exercise that leaves you gasping for air.
Moderate exercise is around 5 or 6, while a target level for high-intensity intervals would be around 7 or 8.
It’s also worth noting that beta blockers are no longer considered the first-line therapy for uncomplicated high blood pressure (that is, high blood pressure without any related health problems, such as angina or a past heart attack).
If that’s the case for you, other classes of drugs — such as certain types of calcium-channel blockers that don’t slow the heart rate, ACE inhibitors, or angiotensin-receptor blockers — maybe preferable.
For a list of the different classes of blood pressure drugs and common examples, see see here.
