Fit Fact: Women Have a Different Heart Rate Response to Exercise

It's taken the medical and fitness world some time to figure out that women aren't just small men (and if they'd just read "Men are from Mars, Women are from Venus," they would've known that) but they are getting there. We know that women's bodies work differently from men's - woman have different heart attack symptoms, they tend to lose weight differently and they also have a different response to exercise.

In a recent study experts decided to ask an important question - are the heart rate formulas we use, largely based on men, accurate for women?

The answer: Not really. After some study, they realized that the traditional formula used to calculate maximum heart rate, (220-age or the updated version, 206.9 - (0.67 x age)) actually overestimated maximum heart rate for women.

With this information, experts have come up with a new formula to calculate maximum heart rate for women. 206 - (.88 x age) = MHR

Now, the experts in this study were actually more interested in finding an accurate peak heart rate for women in order to predict future health and to make sure women recovering from heart problems were given the right exercise intensity to recuperate. If the numbers were too high (as the experts suggest in this study), they might be doing women more harm than good by trying to make them work too hard.

Now, I've always promised there would be no math on this blog, but I lied, so bear with me. Let's take a look at how target heart rate zones would be different using the new max heart rate formula along with the karvonen formula. Say you're a 49 year old woman with a resting heart rate (RHR) of 65:

Old Formula

206.9 - (0.67 x 49) = 174
174 - 65 (RHR) = 109
109 * 65% (low end of heart rate zone) OR 85% (high end) = 71 (65%) or 93 (85%)
71 + 65 (RHR) = 136
93 + 65 (RHR) = 158
The target heart rate zone for this person would be 136-158 beats per minute.

New Formula

206 - (.88 x 49) = 163
163 - 65 (RHR) = 98
98 * 65% (low end of heart rate zone) OR 85% (high end) = 64 (65%) or 83 (85%)
64 + 65 (RHR) = 129
83 + 65 (RHR) = 148
The target heart rate zone for this person would be 129-148 beats per minute.

You can see how different these numbers are and this suggests that some women may be struggling to get to a certain intensity, not because they're not in shape, but because their max heart rate has been overestimated.

So, what about you? How does this formula change your numbers and do you think it's more accurate? How heavily do you rely on calculations like this anyway?

Source:

RJ Gibbons, GJ Balady, J Timothy Bricker, at al. Heart Rate Response to Exercise Stress Testing in Asymptomatic Women. The St. James Women Take Heart Project. Circulation. 2002;106:1883.

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