Chances are pretty good that if you regularly read this magazine, you already know a thing or two about your own heart rate; after all, you make a concerted effort to raise it several times a week to improve or maintain your body composition. And if you’ve spent any time in a group exercise class, you also may know how to find your heart rate: Lightly place your index and middle finger on the palm side of your opposite wrist until you feel a pulse. Keeping your eyes on a clock for six seconds, count the number of beats and then add a zero to the end to find your beats per minute. You may even know the mathematical formula to determine your maximum heart rate (220 minus your age) and be able to figure out your target training intensity (220 minus your age, multiplied by the percentage you’re aiming for). For example, a 38-year-old woman has a maximum heart rate of 182 (220 – 38). To train at between 65 and 75 percent of her MHR, she’d try to keep her beats per minute (or bpm) between 118 and 137 (220 – 38 x .65 and .75, respectively).
Those are the basics, and at best, they’ll give you a ballpark figure that you can try to meet in the gym. But if you get to know just a little bit more about your own heart rate, you can pinpoint your target heart rates more accurately — and reach your goals more quickly.
To do that, you need to find your heart-rate reserve, which is, simply put, the difference between MHR and resting heart rate. To calculate your RHR, take your pulse for one minute right after waking up in the morning, before you get out of bed. (If you have a severely annoying alarm clock, turn it off and lie quietly for five minutes, then take your pulse.) Do this five mornings in a row, then calculate the average. The result is your RHR (and the better your cardiovascular fitness, the lower your RHR will be). Then you can use it in what’s called the Karvonen formula:
(HRR x training percentage) + RHR = THR.
Say our 38-year-old woman finds she has an RHR of 55 and still wants to train at between 65 and 75 percent of her MHR. She would first find her heart-rate reserve by subtracting her RHR from her MHR (182 – 55) and get 127. To find her target heart-rate range, she’d do the following calculations:
(127 x .65) + 55 = 138 bpm (127 x .75) + 55 = 150 bpm
Notice the results here are significantly higher than the more widely used formula mentioned in the second paragraph of this story. By taking her RHR into account, that 38-year-old woman just discovered she’s able to push herself harder than she thought she could — translating into better cardiovascular and physique results in less time.
Yes, that’s a lot of math, and it can be pretty difficult to take your distal pulse in your wrist while jogging on a treadmill — which is why virtually every piece of cardio equipment you find in a commercial gym comes equipped with a heart-rate monitor. But don’t trust it, Jim Ryno says, a celebrity trainer and owner of LIFT, a chain of private personal-training gyms in New Jersey and New York City.
“They test them on bigger guys who are in shape. So the numbers are always going to be inflated,” he says. Even when you program your weight into the machine, “there’s no way it can take into account your actual intensity.”
Better to invest in a wireless heart-rate monitor you can program with your real information, and leave the sweaty handgrips to the next big guy who comes along.
Next month: How to choose your target heart-rate zone.
SIDEBAR: Cardiac Key
BPM: beats per minute
MHR: maximum heart rate
THR: target heart rate
RHR: resting heart rate
HRR: heart-rate reserve