Tuesday, July 6, 2010

A Revised Myth

The New York Times reports that according to a new mathematical formula used to calculate a woman's maximum heart rate, women who are trying to push themselves hard during exercise can actually push a little less hard:
[R]esearchers at Northwestern Medicine in Chicago announced a new formula for calculating a woman’s maximum heart rate, a measure commonly used by athletes to pace themselves and monitor their progress. In a study of nearly 5,500 healthy women, scientists discovered that a decades-old formula for calculating heart rate is largely inaccurate for women, resulting in a number that is too high.

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

The commonly used formula subtracts a person’s age from 220. But based on the data collected in the Chicago 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 runners, cyclists and other exercisers obsessively monitor their heart rates by taking their pulse and rely on the old formula to gauge the intensity of the workout. 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.

But 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.
But if you're someone who's "obsessively" checking your heart rate during your workouts, you know you can stop, right? Constant monitoring of your heart rate is unnecessary. If you exercise regularly, you can judge how hard you're pushing yourself, and can instinctively ramp your intensity up or down accordingly. Unless you're: (1) completely new to exercise and want to get a baseline sense of how hard you're working, or (2) a highly-specialized athlete doing some very specific training to gain a particular (marginal) boost in performance, your heart rate monitor's just a high-tech distraction from your workout.

Besides, as I've mentioned before, the "target heart rate zones" posted on treadmills and elliptical machines are utter bullshit. (Want more on this subject? Read this and this.)

So in the end, what does the new formula for calculating women's max heart rates tell us?

Not too much.