Maximum Heart Rate
As I wrote in my blog post from last week I have some patients who are absolute exercise fiends. In fact, I saw one today who took to heart my rebuke of his obesity and embarked on a diet and exercise regimen that has shaved off nearly 60 pounds over the last 6 months.
Cardiac patients who exercise actively are often concerned with their resting and exercise heart rates. This probably wasn’t much of an issue years ago, but with the ubiquitous presence of devices to measure pulse rate people are much more aware of what their heart is doing. The more aggressive exercisers sometimes ask me to tell them what a safe maximum heart rate would be for someone in their condition. I had a patient just last week tell me a friend told him he shouldn’t get his heart rate above 110 beats per minute even though the cardiac rehab nurses taught him he could go higher.
I’ll start with a little context. We measure heart rate in beats per minute with a normal resting range being about 50 to 90. With exercise we expect the rate to rise based on factors such as age, level of exertion, medications and physical conditioning. We frequently refer to heart rate in terms of percentage of maximum predicted heart rate (MPHR). We can roughly predict how fast your heart can race at peak exertion with the equation 220 – age. Using this formula on me I would expect a MPHR of 190 beats per minute. Take this equation with a grain of salt, however, since I have seen many patients who can easily exceed their MPHR.
When we do treadmill stress testing we try to push the patient to about 85% of their MPHR. That’s generally a universally-accepted threshold that guarantees an adequate level of stress. Some people attain that level within the first couple of minutes on the treadmill, while others may not get there until they are in the more advanced stages of the test. In general, patients who are more physically fit can go harder and longer on the treadmill before they reach 85% of their MPHR.
So let’s answer the question: How high should a cardiac patient push his or her heart rate during routine exercise? I know what advice I give my patients (summarized at the bottom) but I sought out several second opinions. I queried some of my esteemed partners on what advice their give their patients on this subject and was surprised to learn that most of them rely on their clinical judgment (rather than formulas) to guide their suggestions.
Dr. Shirley Huerter, a youthful but seasoned heart expert and Creighton alum, modestly couched her response by saying “You will hate my very un-scientific answer,” which led me to believe that she, like I, uses common sense to drive her recommendations and suggests that patients ignore heart rate all together. Her advice:
“I tell him that he should be short of breath, but able to carry on a conversation while exercising. If he couldn’t talk to the person next to him, then he is working too hard and if he isn’t short of breath at all, then he’s not working hard enough. This allows patients to gradually increase exercise as their cardiovascular fitness improves, and still use the same guideline.”
It turns out that this is the exact same advice I give to my patients.
Dr. Atul Ramachandran, another Creighton grad and father of two, also resists putting a peak level on heart rate with exercise. He adds that he feels higher heart rates should be sought if a patient really wants to improve their aerobic fitness rather than just burn calories.
Both Drs. Jeffrey Carstens (an interventional cardiologist who did his training in the Navy) and Joseph Thibodeau (a UNL man with cardiology training in Kansas City) both advocate a treadmill stress test prior to clearing a patient for full exercise. Dr. Carstens adds:
“If I have a patient who wants to exercise vigorously—to, say, greater than 85% MPHR—then I will usually do a stress test on them prior to clearance, to look for any evidence of ischemia (inadequate blood supply to the heart muscle due to blockage of the coronary blood vessels). If they don’t want to really push it, I am pretty comfortable with 70-75% routinely.”
After looking at the responses of my partners I’ve come to the following conclusions:
- If you are starting an exercise program after a life of sedentary inactivity, or if you have risk factors for heart disease and don’t usually exercise, you should probably talk to your doctor and consider undergoing a treadmill stress test.
- There is likely no limit to how high you can push your heart rate with vigorous exercise if you feel good, have no chest pain, and have been cleared by your doctor.
- Just because you’ve had heart problems doesn’t mean that you need to forever curb your activity level. Ask your cardiologist specifically if you are allowed to exercise without restriction—most patients are.
- Use common sense when you exercise and back off if you think you are having a problem. Otherwise, go out there and whip yourself into the best shape of your life!