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Correction Appended
Donald Kirkendall, an exercise physiologist at the University of = North=20 Carolina, will never forget the time he put a heart-rate monitor on a = member of=20 the United States rowing team and asked the man to row as hard as he = could for=20 six minutes.
The standard formula for calculating how fast a human heart can beat = calls=20 for subtracting the person's age from 220. The rower was in his = mid-20's.
Just getting the heart to its actual maximum rate is an immense = effort and=20 holding it there for even a minute is so painful that it is all but=20 inconceivable for anyone who is not supremely motivated, Dr. Kirkendall = said.=20 But this rower confounded the predictions.
''His pulse rate hit 200 at 90 seconds into the test,'' Dr. = Kirkendall said.=20 ''And he held it there for the rest of the test.'' A local cardiologist = was=20 looking on in astonishment and told Dr. Kirkendall, ''You know, there's = not a=20 textbook in the world that says a person could have done that.''
But maybe, some physiologists and cardiologists are saying, the = textbooks are=20 wrong.
The question of how to find maximum heart rates is not just of = academic=20 interest, medical experts say. The formula for calculating the maximum = rate has=20 become a standard in cardiology and in fitness programs, and an entire = industry=20 has grown up around it, with monitors sold to individuals and built into = exercise equipment.
''There is a need, a clinical and societal need, to estimate the = maximum=20 heart rate,'' said Dr. Douglas Seals, an exercise physiologist at the = University=20 of Colorado.
Doctors use the formula when they test patients for heart disease, = asking=20 them to walk on treadmills while the speed and incline are gradually = increased=20 until their heart rates reach 85 percent of the predicted maximums.
The idea is to look for signs, like chest pain or a sudden drop in = the heart=20 rate, indicating that the heart is not getting enough blood. But if = doctors=20 underestimate how fast the person's heart can beat, they may stop the = test too=20 soon, Dr. Seals noted.
Personal trainers and exercise instructors design fitness programs = around the=20 maximum heart rate, often telling people to wear heart rate monitors and = then to=20 exercise at 80 to 90 percent of the maximum in brief spurts to build = aerobic=20 capacity and at 65 percent to 75 percent to build endurance.
Some heart monitors built into exercise machines even shut the = machines down=20 if an exerciser exceeds 90 percent of the predicted maximum. But if the = heart=20 rate formula is wrong, these exercise prescriptions are misguided.
''If you're trying to improve their aerobic fitness or to train for = certain=20 endurance events, then you want to know with a reasonable accuracy what=20 intensity you're exercising at,'' Dr. Seals said. ''If your estimate is = 10 or 20=20 beats too low, then you're pretty far off.''
Exercise physiologists say, however, that being pretty far off is = more common=20 than most people expect.
''The more information we have, the more we realize that that formula = is just=20 a very rough consideration,'' said Dr. Jack H. Wilmore, an exercise = physiologist=20 at Texas A&M.
And while Dr. Seals is now proposing a new formula to use as a = general guide,=20 he and others say it is simplistic to rely on a single formula to = predict the=20 maximum heart rates of individuals.
The common formula was devised in 1970 by Dr. William Haskell, then a = young=20 physician in the federal Public Health Service and his mentor, Dr. = Samuel Fox,=20 who led the service's program on heart disease. They were trying to = determine=20 how strenuously heart disease patients could exercise.
In preparation for a medical meeting , Dr. Haskell culled data from = about 10=20 published studies in which people of different ages had been tested to = find=20 their maximum heart rates.
The subjects were never meant to be a representative sample of the=20 population, said Dr. Haskell, who is now a professor of medicine at = Stanford.=20 Most were under 55 and some were smokers or had heart disease.
On an airplane traveling to the meeting, Dr. Haskell pulled out his = data and=20 showed them to Dr. Fox. ''We drew a line through the points and I said, = 'Gee, if=20 you extrapolate that out it looks like at age 20, the heart rate maximum = is 200=20 and at age 40 it's 180 and at age 60 it's 160,'' Dr. Haskell said.
At that point, Dr. Fox suggested a formula: maximum heart rate equals = 220=20 minus age.
But, exercise physiologists said, these data, like virtually all = exercise=20 data, had limitations. They relied on volunteers who most likely were = not=20 representative of the general population. ''It's whoever came in the = door,'' Dr.=20 Kirkendall said.
In addition, he and others said, gauging maximum heart rates for = people who=20 are not used to exercising is often difficult because many prematurely = stop the=20 test.
As the treadmill hills get steeper, people who are not used to = exercise will=20 notice that their calves are aching. ''They will say they can't go any=20 further,'' Dr. Kirkendall said.
In addition, Dr. Wilmore, the exercise physiologist, said it was = clear from=20 the scattered data points that maximum heart rates could vary widely = from the=20 formula. ''If it says 150, it could be 180 and it could be 120,'' Dr. = Wilmore=20 said.
But the formula quickly entered the medical literature. Even though = it was=20 almost always presented as an average maximum rate, the absolute numbers = took on=20 an air of received wisdom in part, medical scientists said, because the = time was=20 right.
Doctors urging heart patients to exercise wanted a way to gauge = exercise=20 intensity. At the same time, exercise gurus, promoting aerobic exercise = to the=20 public, were asking how hard people should push themselves to improve = their=20 cardiovascular fitness. Suddenly, there was a desire for a simple = formula to=20 estimate maximum heart rates.
''You tell people to exercise at a moderate intensity,'' Dr. Haskell = said.=20 ''Well, what's a moderate intensity?''
Soon, there was a worldwide heart-rate monitor industry, led by Polar = Electro=20 Inc, of Oulu, Finland, selling more than 750,000 monitors a year in the = United=20 States and citing the ''220 minus your age'' formula as a guide for=20 training.
The formula became increasingly entrenched, used to make graphs that = are=20 posted on the walls of health clubs and in cardiology treadmill rooms,=20 prescribed in information for heart patients and inscribed in textbooks. = But=20 some experts never believed it.
Dr. Fritz Hagerman, an exercise physiologist at Ohio University, said = he had=20 learned from more than three decades of studying world class rowers that = the=20 whole idea of a formula to predict an individual's maximum heart rate = was=20 ludicrous. Even sillier, he said, is the common notion that the heart = rate is an=20 indication of fitness.
Some people get blood to their muscles by pushing out large amounts = every=20 time their hearts contract, he said. Others accomplish the same thing by = contracting their hearts at fast rates. As a result, Dr. Hagerman said, = he has=20 seen Olympic rowers in their 20's with maximum heart rates of 220. And = he has=20 seen others on the same team and with the same ability, but who get = blood to=20 their tissues by pumping hard, with maximum rates of just 160.
''The heart rate is probably the least important variable in = comparing=20 athletes,'' Dr. Hagerman said.
Heart rate is an indicator of heart disease, said Dr. Michael Lauer, = a=20 cardiologist and the director of clinical research in cardiology at the=20 Cleveland Clinic Foundation. But, he added, it is not the maximum that = matters:=20 it is how quickly the heart rate falls when exercise is stopped.
An average healthy person's heart rate drops about 20 beats in a = minute and=20 the rates of athletes ''nose dive by 50 beats in a minute,'' Dr. Lauer = said.
In three recent studies, Dr. Lauer and his colleagues found that = people whose=20 rates fell less than 12 beats within a minute after they stopped = exercising=20 vigorously had a fourfold increased risk of dying in the next six years = compared=20 with those whose heart rates dropped by 13 or more beats.
Dr. Lauer pays no attention to the standard formula when he gives = treadmill=20 tests. More than 40 percent of patients, he said, can get their heart = rates to=20 more than 100 percent of their predicted maximum. ''That tells you that = that=20 wasn't their maximum heart rate,'' Dr. Lauer said.
The danger, he said, is that when doctors use that formula to decide = when to=20 end a treadmill test, they can inadvertently mislead themselves and = their=20 patients. Some patients may be stopping too soon and others may seem to = have a=20 heart problem because they never can get to what is supposed to be their = maximum=20 rate.
''Some people are being pushed and others are not,'' Dr. Lauer said. = ''In my=20 view, that is unacceptable.''
Yet, Dr. Seals said, many doctors want some sort of guide for = estimating=20 maximum heart rates for treadmill tests. And many people who want to = increase=20 their fitness crave a general formula.
So Dr. Seals and his colleagues decided to take another stab at = finding an=20 equation.
In a study published in the March issue of The Journal of the = American=20 College of Cardiology, Dr. Seals and his colleagues devised a new = formula:=20 maximum heart rate equals 208 minus 0.7 times age. They used published = studies=20 involving 18,712 healthy people and data from 514 healthy people they = recruited.=20 Their formula gives much higher average maximum heart rates for older = people,=20 with the new and old heart rate curves starting to diverge at age = 40.
But raising doubts about the heart rate formula is unlikely to lead = people to=20 abandon it, exercise physiologists say. What would they do without = it?
''I've kind of laughed about it over the years,'' Dr. Haskell said. = The=20 formula, he said, ''was never supposed to be an absolute guide to rule = people's=20 training.'' But, he said, ''It's so typical of Americans to take an idea = and=20 extend it beyond what it was originally intended for.''
Photos: Dr. Douglas Seals, an exercise physiologist, watches as Chris = Bell=20 raises his heart rate on a treadmill. (Kevin Moloney for The New York = Times)(pg.=20 F1); Dr. William Haskell compares the heart rate of Jeff Myll, who wears = a Polar=20 Electro watch monitor, available commercially, with a reading from an = EKG.=20 (Peter DaSilva for The New York Times)(pg. F8)
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