Adding up heartbeats and understanding heart rates
I receive a lot of emails from readers, which are wide-ranging in topic. Sometimes they’re from readers who agree with me while others take issue with what I’ve written. Some ask provocative questions or provide a unique view or stance on an issue I had not considered, which often can inspire a new column.
I also receive emails where readers want to educate me on an issue on which they disagree with me. Recently I received an email from a reader who slammed me for advocating exercise. His position was that the heart is born with a set number of beats, and when that number is reached, the heart stops.
At first, I assumed this was a joke, but then I realized he was serious, had done some research on the subject, and referred to it as the “Finite Heartbeat Theory.”
He wrote that each of us gets a total of 2.5 billion heartbeats and the faster your heart beats, the faster you use them. This means exercise that can double, or even triple, your resting rate is a foolish waste of important “life-sustaining” heartbeats, which means you will die sooner.
For proof, he referred to the premature death of Jim Fixx. Fixx was a runner who wrote a best-selling 1977 book “The Complete Book of Running,” which inspired millions of folks to get moving. Ironically, in 1984, Fixx died at age 52 of a heart attack during his daily 10-mile run. The reader saw this as proof that his daily runs used up his heartbeats prematurely.
He then cited a research study on 5,000 men over 16 years that reported the higher the resting heart rate, the earlier they died. Specifically, with a resting heart rate of 81-90 bpm the chances of dying during that period were twice as high as those with a resting heart rate under 50 bpm, and three times higher with a resting heart rate over 90.
Let’s unpack this argument.
Is there an average amount of lifelong heartbeats?
One way, I assume, to guesstimate total lifelong heartbeats would be to use a typical resting heart rate of 72 beats per minute for adult males. Multiply this times 60 minutes in an hour, times 24 hours a day, times 365 days a year, and times a life expectancy of 73 years. Do this, and you get a big stockpile of heartbeats that, according to the “Finite Heartbeat Theory,” should be spent carefully.
Unfortunately, the logic breaks down when considering that the resting heart rate of women is about 10 beats higher than men. This means, according to the theory, women should use up their allotted heartbeats faster than men and die sooner, when in fact the opposite oc
curs, and women outlive men.
Regarding the premature death of Fixx, it wasn’t because he used up his heartbeats too quickly during daily exercise. Before he took up running, he followed an unhealthy lifestyle that included chain smoking, plus he had a family history of heart disease. Thus, a case can be made that running prolonged his life, but ultimately, it could not overcome the unhealthy heart disease seeds he planted at an early age.
In addition, the heavy exercise routine Fixx followed would condition his heart to beat much more slowly at rest. This means that even though his heart rate was higher during exercise, for the remaining 23 hours a day at rest, the much lower heart rate would add up to far fewer heartbeats per day.
And finally, regarding the research suggesting that a higher resting heart rate caused folks to die earlier than those with a lower resting heart rate, this likely is true. However, it has nothing to do with using up heartbeats faster. Instead, a lower resting heart rate can imply several meanings, including less body fat and a more physically active lifestyle which help protect against heart disease.
What is the maximal heart rate?
I also recently received an email asking how high is the maximal heart rate (HRmax). That depends, and age is a big factor as the maximal rate declines with age. For example, in someone 20 years of age, 200 beats per minute (bpm) is typical, with a range of 190 to 220, although 220 would be quite high and rare. For someone 60 years of age, the HRmax would be about 173 bpm.
Because it’s difficult to reach HRmax, there are age-related prediction equations available. The old standby is 220 – age. This has been around for a long time and was accepted without any real evidence to support it. It works pretty well for young folks but tends to underpredict for older individuals. The predictions for folks ages 20 and 60 would be 200 bpm and 160, respectively. The 200 is a good prediction, but the 160 is too low.
There are more accurate prediction equations. The one I prefer is 200 – 0.67 (age – 20). As you can see this equation would predict the same HRmax of 200 for a 20-year-old. However, for someone who is 60, the formula works out to be 200 – 27 = 173 bpm which is much more likely.
Why does HRmax decline with age? A long-standing explanation was that with age there are structural changes in the heart muscle that no longer can support a very high heart rate. The most recent studies, however, suggest that the pacemaker of the heart changes and can no longer trigger stimulatory impulses as rapidly.
Reach Bryant Stamford, a professor of kinesiology and integrative physiology at Hanover College, at stamford@hanover.edu.