Forget the heart rate monitors, LED displays of calories burned and other gee-whiz measures of your exercise intensity. The best judge of whether your workouts are hard enough to protect your heart appears to be you, according to a study to be published in the March 4 issue of the American Heart Association's journal Circulation.

Researchers investigating the relationship between exercise habits and the occurrence of coronary heart disease surveyed more than 7,300 male Harvard graduates whose mean age was 66. Instead of relying on standardized measures of exercise intensity, however, I-Min Lee of the Harvard School of Public Health and her team asked participants to describe how intense they felt their workouts were.

"Some men," says Lee, "did not conform to conventional wisdom [in terms of exercise intensity] but thought they were exercising at a high level. [Still, they] had a reduced chance of [coronary heart disease]." Overall, the study shows lower rates of disease among men who felt they were exercising at moderate or greater intensity, even if their actual levels fell below definitions used by the Centers for Disease Control and Prevention and the American College of Sports Medicine.

One commonly used scale -- metabolic equivalents, or METs -- ranks different exercises by the energy each requires. Jogging, for example, requires more than six METs; brisk walking requires three or more. A three-MET exercise is the generally accepted minimum to derive health benefits. The trouble with that system, says Lee, is that it doesn't recognize that one person's moderate exercise could be another's vigorous workout: "Brisk walking might be fine if you're fit, but some people, like my 93-year-old grandmother, are unable to do even that," she said.

The study suggests, says Lee, that exercise intensity is relative to a person's abilities. As long as your workout feels to you like it's three METs (or greater), you're doing yourself good.

But if you didn't graduate from Harvard? Or you're a woman?

Lee can't say for sure -- her study group was too limited -- but she feels certain her study has wide applicability: "It's encouraging for individuals who have trouble reaching standard levels. . . . Even if you're at the bottom of the [fitness] spectrum, you can do something manageable."

-- Matt McMillen

exertiondurationmetabolic equivalentsMETs