On an airplane traveling to the meeting, Dr. Haskell pulled out his data and showed them to Dr. Fox. ''We drew a line through the points and I said, 'Gee, if you extrapolate that out it looks like at age 20, the heart rate maximum is 200 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 minus age.

But, exercise physiologists said, these data, like virtually all exercise data, had limitations. They relied on volunteers who most likely were not representative of the general population. ''It's whoever came in the door,'' Dr. Kirkendall said.



Heart rate is an indicator of heart disease, said Dr. Michael Lauer, a cardiologist and the director of clinical research in cardiology at the Cleveland Clinic Foundation. But, he added, it is not the maximum that matters: 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 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 rates fell less than 12 beats within a minute after they stopped exercising vigorously had a fourfold increased risk of dying in the next six years compared with those whose heart rates dropped by 13 or more beats.