You’re sweating, you’re panting, your heart is beating hard—yet you’ve only burned half as many calories as your friend jogging on the treadmill next to yours.

Still, your workout may be just as good for your heart as your friend’s, according to a study released this week by a professor at the School of Public Health.

The study, published in the journal Circulation, suggests that a person’s perceived level of exertion—not just the number of calories burned—is an indicator of how much exercise is necessary to minimize one’s risk of heart disease.

7,337 male Harvard College graduates were followed from 1988 to 1995. Those who perceived their workout levels to be “strong” less often developed coronary heart disease than those who reported less intense workouts.

Currently, universal workout recommendations suggest exercising enough to burn 1,000 calories per week. An elderly person may not be physically able to engage in exercise which will burn this many calories, but, according to the study, a lighter workout tailored to his or her ability will suffice.

According to the study’s lead author, Associate Professor of Epidemiology I-Min Lee, the study doesn’t absolve the couch potato. But the same grueling workout routine might not be right for everyone.

“Don’t feel discouraged if, while exercising, you’re not carrying out the activities that are recommended,” Lee said. “So long as you feel [that the workout] is hard for you, you will gain benefit with regard to heart disease.”

The study measured the relative intensity of participants’ workouts by asking them to rate their level of exertion on the Borg scale which ranges from zero (no exertion) to ten (almost maximal exertion).

Previous studies had relied on an absolute scale of intensity that doesn’t account for differences in participants’ fitness.

A fit person may rank a 12-minute mile as a moderate-intensity physical activity, matching the absolute intensity scale exactly. The relative and absolute intensity scales diverge, however, for older or unfit people, who will perceive the same physical activity as strong-intensity or even impossible.

According to the study, the results suggest that “physical activity recommendations need to be tailored to the individual and that global requirements...may not be appropriate, especially for older persons.”

However, the authors of the study do recommend that those who can should follow the universal recommendation of burning 1,000 calories a week.