Most medical organizations recommend that an adult’s resting heart rate should be between 60 and 100 beats per minute. However, many of us in the Spartan community have a low resting heart rate. Mine is usually around 54.
In medical terms, a low heart rate is known as bradycardia. It can be a problem . . . sometimes. So should you be worried if your resting heart rate is below 60 beats per minute?
An excessively slow heartbeat can mean that your heart does not deliver enough oxygen and other nutrients throughout your body. This lack can cause symptoms including dizziness, fatigue, sweating, nausea, and fainting.
When bradycardia presents with these kinds of symptoms, there will also be some kind of medical issue underlying it. Sometimes this can be a temporary factor such as drug use—particularly beta blockers—or an electrolyte imbalance. More seriously, it can be caused by a more lasting condition such as an autoimmune disorder, neurological disorder, or heart disease. Bradycardia is usually acquired, rather than congenital, and is more common in older patients.
As mentioned earlier, bradycardia is medically defined as a heart rate below 60 bpm. However, symptoms usually don’t appear until the heart rate is below 50 bpm. Now, you might ask—is it really a problem if you feel OK? Maybe, but maybe not.
Remember that 60–100 beats per minute guideline? That was for the average, mostly sedentary person. Athletes often have heart rates as low as 40 bpm. People who are not athletes, but who exercise more than average and stay in good shape, commonly have a low resting heart rate in the 50s without suffering any health problems. In fact, some researchers have suggested that the normal range should be defined as 50–90 bpm, rather than 60–100 bpm, since 50–90 is the range that best characterizes healthy non-athletes.
Studies have consistently shown that a lower resting heart rate, at least down to 40 bpm, is associated with a longer life span, both in comparisons between individuals and between species. For every 20 additional beats per minute of resting heart rate, mortality increases by 30–50 percent.
The association between a low resting heart rate and lifespan appears to work through at least two distinct mechanisms. First and most obviously, a lower heart rate is associated with a healthier heart. People with a low resting heart rate are far less likely to die of cardiac illness.
Second, a lower heart rate is associated with a slower metabolic rate. A slower metabolism will mean that you’ll have less energy, be less active, and possibly also be more prone to weight gain if you overeat—but since your body is running more slowly, it will age more slowly. In effect, everything is slowed down—whether this is worth the tradeoff is a matter of individual preference.
Now, you may notice a contradiction there. A slower heart rate is associated with a slower metabolism, but also with being athletic—yet athletes have faster metabolisms, not slower. To understand why this is, you need to look at other factors besides just heart rate.
As mentioned earlier, a slower heart rate generally means that fewer nutrients and less oxygen are being delivered throughout your body. At least, all other factors being equal, that’s what it would mean—but all other factors are never really equal.
In order to know how well your blood is delivering nutrients throughout your body, you need to know several things. First, you need your heart rate, obviously. Second, you need to know your stroke volume—how much blood gets pumped through your heart per heartbeat. A higher stroke volume means that high blood flow can be maintained at a relatively low heart rate. Unfortunately, stroke volume is difficult to measure non-invasively, so it isn’t typically measured in routine check-ups unless the patient has heart disease.
Third, you want to know how many red blood cells you have. The technical term for this is hematocrit—the percentage of your blood volume that consists of red blood cells. A typical hematocrit level is 47 percent plus or minus 5 percent for men and 42 percent plus or minus 5 percent for women. A lower hematocrit would mean that your heart would need to pump more blood to oxygenate the body. A high hematocrit would mean that you can safely live with a lower heart rate, but it would also mean that your blood is getting excessively thick, which can cause problems of its own.
In addition to how many red blood cells you have, you would want to know how much oxygen your red blood cells are carrying—higher oxygen saturation means that less blood flow is needed to keep the body fueled up.
You also want to know your heart rate variability. Your heart rate should be faster when you inhale and slower when you exhale, so high heart rate variability is a sign of good cardiac health.
Finally, you want to know your blood pressure. If your heart rate is low but your blood pressure is normal, that implies that, low or not, your heart rate is sufficient to keep your blood flowing normally.
The Bottom Line: You’re Probably OK, But...
You're probably OK, but it's worth talking to your doctor.
To recap: you’re probably fine if your resting heart rate is over 50, or 40 if you’re an athlete. You’re also probably fine if you don’t feel any of the symptoms of bradycardia, like dizziness, fatigue, sweating, or fainting.
But if you’re close to those values and still worried, it’s worth talking to your doctor and getting a few simple tests, including hematocrit, blood oxygen content, electrolyte levels, heart rate variability, and blood pressure.
If you’re a health nut, it’s easy to obsess over isolated measures like your heart rate. The bottom line is, if your low heart rate is a problem, you’ll probably be feeling it. If you’re exercising regularly and have a low heart rate, but you feel good and every other measure of cardiac health looks good, you’re fine.