The Maximum Heart Rate MythYou've probably been told that the best way to predict your maximal heart rate — the maximum number of times your heart can beat each minute — is to subtract your age from the number 220. But where does the formula for calculating your maximum heart rate actually come from? And can it be trusted? Although scientists have been attempting to predict maximal heart rates since the late 1930's, the 220 minus age formula originated in the late sixties when Dr. William Haskell, an exercise physiologist who is now at Stanford University, and Sam Fox, a cardiologist, provided a formula for maximum heart rates for people who were having treadmill stress tests for heart disease. In subsequent years, the formula has become immortalized in charts on every gym wall, on cardiovascular exercise machines, and even in medical textbooks. But when Gina Kolata, science writer for The New York Times, did a little detective work, she was astonished to find that the formula was meant only as a rough guideline — not as the precise measurement often used by serious athletes to gauge their progress via heart rate monitors. In her book Ultimate Fitness: The Quest for Truth about Exercise and Health, Kolata asked Dr. Haskell to tell his story... It was 1968, Haskell said, and he had recently gotten his Ph.D. in exercise physiology and was employed by the U.S. Public Health Service, one of thousands of doctors and scientists who work in government offices and laboratories under the direction of the Surgeon General. His job put him under the supervision of Sam Fox, a doctor who was the head of a major heart-disease prevention program in the Public Health Service. Fox had been invited to give a talk at a World Health Organization meeting on the use of exercise testing to detect heart disease. So he asked Haskell to help him prepare, sending him to the library to gather papers in which people of different ages had been tested to find their maximum heart rates. Haskell found seven papers and plotted the data on a piece of graph paper. Shortly afterward, while they were sitting together on a long airplane ride, Haskell pulled out his plot and showed it to Fox. "We drew a line through it and I said 'Gee, if you extrapolate that out, it looks like at twenty, your maximum heart rate is two hundred, at age forty it's a hundred and eighty, at sixty it's one-sixty..." Fox, he says, turned to him and said, "It looks like two-twenty minus your age." In 1971, Fox and Haskell published a graph based on ten studies, rather than the original seven, along with their formula. They concluded, once again, that the formula maximum heart rate equals 220 minus age best fit the data. More recently, Dr. Douglas Seals, an exercise physiologist at the University of Colorado, tried to improve the formula, gathering data from 351 published studies involving 18,712 people [1]. To that he added his own data from studies involving 514 men and women, aged 18 to 81. Seals found that a person's maximum heart rate is independent of both physical fitness and gender but does depend on how old they are. His research, published in the American Journal of Cardiology, shows that the traditional formula of 220 minus age overestimates the maximum rate in young adults, does a pretty good job for people who are around forty years old, and then increasingly underestimates the maximum rate as people get older. A much more accurate formula, he says, is 208 minus age times 0.7. The table below shows you the difference between predicted maximal heart rates obtained using both the new and old equations.
Even with that formula individuals vary so much that someone's true maximum could be as much as twenty beats per minute higher or lower than the number the formula provides. Yet Seals, despite his impressive and exhaustive effort to get accurate data and derive a better formula, failed to supplant the old equation suggested by Haskell and Fox. Haskell is a bit taken aback by the way the heart-rate formula has come to be viewed almost as a physical law. "I've kind of laughed about it over the years," he says, adding, "It's typical of Americans to take an idea and extend it way beyond what it was intended for." When he and Fox proposed the formula, they never intended to give an absolute number for athletes or people who are used to exercising vigorously. Interestingly, when Dr. Robert Robergs recently analyzed the data on which the original formula was based, he ended up with a totally different equation! In fact, it's clear from the widely scattered data points on the graphs of heart rates that any individual's maximum rate can vary widely from what that formula predicts, by as many as thirty beats per minute higher or lower. In other words, if it says 140, it could be as high as 170 or as low as 110. And that means that what you calculate as your training zone could be completely wrong.
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