Using Maximal Heart Rate to Measure Exercise Intensity – Is the Formula Flawed?

November 24, 2013

by Cathe Friedrich

There are a number of ways to monitor the intensity of a workout. One is to know your maximal heart rate and compare your heart rate during exercise to that value. This will let you determine at what percentage of your maximum heart rate you’re exercising. If you’re exercising aerobically, your heart rate should be at 50% of your maximal heart rate or greater at the very minimum. Below that, you’re not going to get cardiovascular benefits and if you’re in shape you need to work out at an even higher intensity to get the benefits. If you’re doing a high intensity workout, your maximum heart rate might be as high as 95% or more of your maximum heart rate during the active intervals. Your exercise heart rate relative to your maximum heart rate gives you an idea of how hard you’re working.

There’s a simple formula that some trainers use to calculate maximum heart rate. It’s 220 minus your age in years. The problem is this formula isn’t really all that accurate, especially for women. The BEST way to determine your maximal heart rate is through a stress test carried out in a controlled environment but that’s not practical for most people.

According to a study published in the journal Circulation, the 220 minus age formula isn’t the best way to calculate maximal heart rate if you’re female. Based on their research. there’s a more accurate formula for estimating maximal heart rate for women:

Maximal Heart Rate: 206 – 88% of your age

It’s a little harder to calculate in your head than the traditional 220 – age formula, but based on exercise stress testing of healthy women this formula is more accurate representation of maximal heart rate for women than the 220 – age formula, although the original formula is still accurate for men. The 220 – age formula actually overestimates a woman’s maximal heart rate. If you’re a woman, 206 – 88% of your age more closely approximates your true maximal heart rate.

Here are some other interesting facts about maximal heart rate and how it affects your workout:

Maximal heart rate refers to the maximum number of times your heart can contract per minute.

Your maximal heart rate isn’t a measure of your level of fitness and doesn’t change as you get fitter. It’s determined by genetics.

Maximal heart rate doesn’t increase with training and doesn’t predict athletic performance. What does change with training is how long you can exercise at your maximal heart rate without being forced to stop from exhaustion. Fitter people can exercise at a higher percentage of their maximal heart rate for longer periods of time than less fit people.

The only way to really determine your maximal heart rate is through exercise stress testing. Any formula you use to calculate is an estimation. For example, the 220 – age formula can be off as much as 15 beats per minute.

There Are Other Ways to Monitor Exercise Intensity

Using percentage of maximal heart rate to estimate exercise intensity works if you have a heart rate monitor. If you don’t there are other ways to monitor intensity:

Talk Test

The talk test is based on the idea that when you exceed your ventilatory threshold, it becomes hard to say more than a few words at a time because you’re breathing so hard. This roughly corresponds to when you’re crossing over your anaerobic threshold and building up more lactic acid. If you’re able to speak in complete sentences during a workout, you’re exercising at a moderate intensity, less than 80% of your maximal heart rate.

Borg Perceived Exertion Scale

To use the Borg scale to measure exercise intensity, you estimate how hard you’re working based on the following scale:

6 No exertion. Essentially at rest.

7 Extremely light exertion. Typing on a keyboard.

9 Very light. Moving papers around on a desk.

11 Light. Walking at a leisurely pace.

13 Feels somewhat hard. Brisk walking but you’re still not out of breath.

15 Hard effort or heavy exertion. You’re breathing hard and your heart is racing.

19 Extremely hard. The most exertion you can sustain for a short period of time.

20 Maximal Exertion. Exercise you can only sustain for a few seconds.

If you have a heart rate monitor, and a heart rate monitor is a good investment if you’re serious about exercise, you can use the maximal heart rate formula to monitor exercise intensity. If you don’t ,the Borg perceived exertion scale and the talk test will give you a pretty good idea of how hard you’re working. If you’re working out at around 11 to 14 on the Borg scale, you’re exercising at a moderate intensity. Once you hit 15, you’re entering the high-intensity zone.

Interestingly, if you multiply your Borg score by 10, it gives you a rough approximation of where your heart rate should be at that level. For example, if you’re exercising at a Borg level of 12, your heart rate would be approximately 120.

The Bottom Line?

There’s more than one way to measure exercise intensity – and you don’t necessarily need a heart rate monitor or to calculate your maximal heart rate. If you do calculate your maximal heart rate, a more accurate formula for females is 206 – 88% of your age.

References:

Circulation. July 2010. “”Heart Rate Response to Exercise Stress Testing in Asymptomatic Women”

Centers for Disease Control and Prevention. “Perceived Exertion (Borg Rating of Perceived Exertion Scale)”

Borg G.A. Psychophysical bases of perceived exertion. Medicine and Science in Sports and Exercise. 1982; 14:377-381.