People all over the world guess every day when they calculate their target heart rate for exercise.
The formula is on every stair stepper, cycle, treadmill and elliptical trainer in every home or gym. It is a formula to determine your target heart rate.
The formula is (220 – YOUR AGE) x Training %.
It’s inaccurate and here’s why.
The year was 1968. Bill Haskell, an exercise physiologist at the U.S. Public Health Service had been given an assignment by his boss Sam Fox, MD. Dr. Fox, a cardiologist, was scheduled to talk at a World Health Organization meeting on exercise and heart disease. Haskell’s job was to collect research on maximum heart rate testing.
All the experts agreed that exercise was important following a cardiac event or if you had heart disease. At the time, no one knew how hard a person should exercise following a heart attack. Haskell assembled the information and plotted the results on a graph. He and Fox studied the graph and discovered a pattern. By drawing a line through the data points, Haskell found that the maximum heart rate at the intervals of 20 years, 40 years and 60 years, was 220 minus the age. Haskell and Fox presented their finding at scientific meetings in Tel Aviv and Tuxedo Park, New York. In 1971, they published their formula that was to become the gold standard for exercise.
The problem with their discovery was the studies were done only on men all under the age of sixty who did not exercise regularly. Haskell and Fox did not actually perform any research. They compiled data from existing studies. So, their formula was not valid for all people. For a valid study, the results must be true in other places, with other people and at other times. Since Fox and Haskell’s work was only on men under the age of sixty, the formula was then only valid for sedentary men under the age of sixty.
Remember, in 1968 there was no heart rate formula. There was no way for a person following a heart attack to know when the heart might be over stressed.
Think about that for a minute. You had a heart attack. You survived. And now, you live in fear of having another one because you have no idea how hard your heart should be taxed.
Haskell and Fox were interested in predicting a maximum heart rate to allow someone following a heart attack to safely exercise again. They never intended for it to be applied to all ages, genders and conditions. It spread quickly and made its way into every piece of exercise equipment, doctor’s office and heart rate monitor in the world because it was simple to understand and easy to use. The formula produced a number that made estimating something very subjective, how hard your body is working, more objective. Numbers are cozy. We feel better when we have numbers to explain, guide or support our decisions.
Haskell and Fox’s formula is not accurate though for someone who exercises regularly. If you are a woman, 40 years of age and use the formula to determine your maximum heart rate, you could be off by up to 30 beats per minute. In most cases, you will exercise at an intensity that is too low. The same is true if you are 65 years of age and exercise regularly. The number guiding you is misleading you.
So, what do you do? How do you determine your maximum heart rate for exercise?
There are two more accurate formulas than the old common way. One in fact just for women.
The first formula is the Karvonen formula. Good for men of all ages and women under the age of 40.
(Max HR- Resting HR) x Training %+ Resting HR= Target HR
Max HR (which is your Max Heart Rate) is 220-AGE (I know this is a little confusing – I didn’t choose the labels).
Let’s say you’re 54 years of age and your resting heart rate is 60 beats per minute. Your Max HR then is 220-54 or 166 beats per minute.
If you want to train at 85%, then you plug these numbers into the formula:
Target HR = (166-60) x .85 + 60
= 150 BPM
Now, the old way, the way just about everyone calculates your Target Heart Rate is 220-AGE x Training %
So, yours would be 141 BPM. You would be under-training. The old method doesn’t take into account your relative fitness which is expressed as your resting heart rate nor does it adjust for a person who has a much higher resting heart rate of, for example, 78 beats per minute.
And the new formula for women over the age of 40:
206-(AGE*.88) = Target Heart Rate
Here’s the thing.
If you’re going to take the time out of your day to train, you might as well train right. Get the most out of it. Know your target heart rate. And, as you get more and more fit, adjust your training to match your new level of fitness.
A word of caution. If you’re using interval training, recognize that you’ll hit your Target Heart Rate fast and likely stay at or near it the whole time. Sustaining 85% of your max for 20 minutes is not where you want to start if you’re new to the idea of training. Start at a lower intensity – 60 or 70% – and work your way up. And if you’ve not exercised in years or ever, get cleared by your doctor first.
Gulati, M., L. J. Shaw, et al. “Heart rate response to exercise stress testing in asymptomatic women: the st. James women take heart project.” Circulation 122(2): 130-7