When working out, you expect your heart rate to go up. In fact, getting your heart rate up during exercise is the best way to track your health and fitness level. But what if your heart rate stays low?
"Normally when you exercise, you want your heart rate to get up to about 60 to 80 percent of your maximum heart rate," says Tamanna Singh, MD, a clinical cardiologist at the Cleveland Clinic. "If your heart rate does not go up enough during exercise, or if it can't mount any response to exercise, you could have a heart problem."
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Defining Maximum Heart Rate
According to the American Heart Association (AHA) your maximum heart rate is the number of heart beats you have per minute when you are at your highest exercise ability. But, as Dr. Singh point out, you only want to reach what's called your target heart rate — 60 to 80 percent of that number. Also, this range gradually lowers with age.
To find the target heart rate range for your age, subtract your age from 220 and then multiply that number by 0.60 and by 0.80 to find the low and high ends of the range. If you are 40 years old, for instance, this formula will tell you that your target range for healthy exercise is about 108 to 144 beats a minute.
Increasing your heart rate during exercise is the best way to increase your heart strength and lower your risk for heart attack, according to Harvard Health Publishing. If you exercise a lot and are in excellent physical shape, it will take more exercise to get to your target range. If you're new to exercise, your heart rate will increase quickly with less exercise.
A Slow Heart Rate: Bradycardia
"Bradycardia is the medical term for a resting heart rate that is less than 60 beats per minute," explains Dr. Singh. "There are two types. If you have a medical condition that slows down your heart, your heart may speed up during exercise, but not enough to reach a target range for exercise. If you have an abnormality of the electrical conduction system of your heart, your heart rate may not increase at all. Exercise could make you pass out."
As the Mayo Clinic explains, bradycardia is a heart rate under 60, but even a heartbeat as low as 40 may be normal for people who are very fit, such as trained athletes. For other people, though, a heart rate under 60 could be a problem, especially if you have such symptoms as:
- Shortness of breath
- Chest pain
- Passing out
"These symptoms are warnings that your body and brain are not getting enough blood supply," says Dr. Singh. "They may get worse during exercise."
Keep in mind, however that your resting heart rate and heart rate while sleeping will naturally be lower than your exercise heart rate.
What Causes Bradycardia?
Mayo Clinic explains that bradycardia is more common in older people with heart damage, incurred from a heart attack or heart surgery, for instance. Infections of the heart — called myocarditis — can also cause bradycardia. "Other common causes include an underactive thyroid gland and medications that slow the heart, like some blood pressure or heart medications," says Dr. Singh.
Also, electrical heart problems can make it impossible for your heart to respond to exercise. Electrical impulses that control your heartbeats start in the right upper chamber of your heart, in a natural pacemaker called your sinus node. From there, electrical signals travel down to the lower chambers of your heart to trigger heartbeats. Sinus node problems can cause dangerous bradycardia, according to the Mayo Clinic.
When to Call Your Doctor
"If your pulse is below 60 most of the time, or if you get tired quickly during exercise and your pulse does not go up as expected, let your doctor know," says Dr. Singh.
Get help right away or call 911 if you pass out during exercise or if you have chest pain and shortness of breath. Your doctor can do tests to find the cause of bradycardia and get you on the right treatment.
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