TARA PARKER-POPE

Researchers at Northwestern Medicine in Chicago recently announced a new formula for calculating a woman¡¯s maximum heart rate, a measure commonly used by athletes to monitor their progress. In a study of nearly 5,500 healthy women, scientists discovered that a decadesold formula for calculating heart rate is largely inaccurate for women, resulting in a number that is too high.

The news may vindicate many women who have struggled to keep up with lofty target heart rates espoused by personal trainers and programmed into treadmill displays.

¡°There¡¯s nothing wrong with achieving a higher heart rate with exercise, and if you can maintain that, it¡¯s fine,¡± said Dr. Martha Gulati, a cardiologist and assistant professor of medicine and preventive medicine at Northwestern, who led the study. ¡°But it might be that some women are getting tired and need to stop because they¡¯re not able to maintain their heart rate at the higher level.¡±

The commonly used formula subtracts a person¡¯s age from 220. But based on the data from the study, the right formula for calculating a woman¡¯s maximum heart rate is a little more complicated: 206 minus 88 percent of a woman¡¯s age.

The findings are significant because many people obsessively monitor their heart rates by taking their pulse and rely on the old formula . The typical goal is to stay within 65 to 85 percent of the estimated maximum heart rate, depending on whether the athlete is trying to build aerobic capacity or increase endurance.

But the new study shows that for women, the number typically derived from the standard formula is far off the mark. Using the old formula of 220 minus age, a 40-year-old woman would achieve an average maximum heart rate of 180 beats per minute. That means her pulse should stay around 153 beats per minute during her workout to achieve a target heart rate of 85 percent.

Based on the new calculation, the same woman¡¯s average maximum heart rate is 171 beats per minute, meaning her desired target heart rate is just 145 beats per minute, 8 beats a minute slower than under the old formula. Although the gap seems small , it can be the difference between an exhilarating workout or a frustrating one that ends in exhaustion.

Dr. Tim Church, an exercise researcher and director of preventive medicine at the Pennington Biomedical Research center in Baton Rouge, Louisana, says that except for elite athletes, heart rate monitoring is not very useful for women or men and can distract from finding an exercise program you enjoy and will stick to.

Everyone kind of has their own natural pace,¡± Dr. Church says. ¡°If you like to work a little harder, then work harder. If you like to work less hard but a little longer, then do that. Find what works for you.¡±