Heart rate and exercise

The Numbers
A Good Heart-Rate Formula Is Hard to Beat
The most widely used measurement has flaws; ‘don’t get hung up on a number’
My heart was racing while working out recently. Was it too fast?
Maximal heart rate—the highest number of times your heart can beat in a minute—is one of the most commonly used measurements in medicine and exercise.
Cardiologists use it to assess heart health. Gym rats use it to gauge how hard to push themselves.
But the formula used most often to predict the maximum is also the worst. It tends to overestimate the top level of exertion for younger people and underestimate it for older people.
New formulas are more accurate, but like the original, the rates they predict may be up to 12 beats too slow, or too fast.
“What I tell people is don’t get hung up on a number,” said Martha Gulati, chief of cardiology at the University of Arizona. “It’s also about symptoms.”
One simple gauge of exertion is the talk test.
“Find the point where you have difficulty talking,” said John Porcari, a professor of exercise and sport science at the University of Wisconsin-La Crosse. “Back off from that pace slightly and you have your sweet spot for exercise intensity.”
Still, exercise is often targeted to a percentage of the maximal heart rate. Moderate exercise intensity is 50% to 70% of the maximum. Vigorous intensity is 70% to 85%.
The traditional formula for predicting maximal heart rate was developed in 1968 by William Haskell, a professor emeritus of cardiovascular medicine at Stanford, and the late cardiologist Samuel M. Fox III.
At the time, they worked for the U.S. Public Health Service and had been looking for a way to measure cardiorespiratory fitness to assist physicians in recommending appropriate physical activity for healthy adults and those with heart disease.
After reviewing the data from 10 published studies, they came up with this formula: 220 minus a person’s age. The result is the predicted maximal heart rate.
According to Dr. Haskell, the studies used to develop the equation were published between 1938 and 1968. All the subjects were men who were generally healthy and ranged in age from 20 to 65. None were on cardiovascular medications, but some probably smoked, and their level of physical activity varied.
The studies followed standard protocols for maximal exercise tests using treadmills or stationary cycles with one interesting exception: One group of researchers tacked a hundred dollar bill to the ceiling in front of the treadmill to motivate participants. The person getting the highest heart rate within each age group got the $100.
That cash incentive, Dr. Haskell surmised, probably accounted for the higher heart rates of those men compared with those in the other studies.
Eventually, researchers noticed flaws in the results delivered by the original equation and began to draft more accurate versions.
Among the first was Hirofumi Tanaka, a professor and the director of the Cardiovascular Aging Research Laboratory at the University of Texas at Austin. His concern was that systematically underestimating the maximal heart rate of older patients, as he had noticed the traditional formula did, could lead to misdiagnoses.
“You might have a condition that wouldn’t be detected because you didn’t push a patient hard enough,” he said.
In 2000, he published this alternative based on a meta-analysis of 351 studies involving 18,712 subjects and validated with a laboratory study of 514 healthy men and women ranging in age from 18 to 81:
208 – (0.7 x Age)
In 2010, Dr. Gulati analyzed 5,437 healthy women ages 41 to 66 and concluded that a different formula should apply to women, whom she found to have lower maximal heart rates than men. Her formula is:
206 – (0.88 x Age)
In 2012, researchers in Norway examined 3,320 healthy men and women and concluded the equation should be:
211 – (0.64 x Age)
In each study, age was by far the best predictor of maximal heart rate, better even than level of fitness, weight, smoking and, in most cases, gender. (Only Dr. Gulati recommended using a different formula for women.)
While the alternatives may be more accurate, the original persists.
Charts that paper gym walls list target heart rates based on it. Top-of-the-line fitness trackers use it to identify exercise zones of different intensities. And many cardiologists use it to prescribe exercise.
Dr. Haskell offers two explanations for the formula’s endurance: It’s adequate for setting exercise targets for generally healthy people. And it’s simple.
In other words, it may be a rough guide. But most of us can apply it no sweat.