When you're already one bucket of sweat deep into a treadmill run, you probably don't also want to pay attention to your heart rate. But figuring out where you want that number to be is easier than you'd think — and it can clue you into a bunch of other information about your body.
Why care about heart rates at all? Well, your heart rate is a measure of how quickly your heart is beating, which indicates that it's pumping oxygenated blood more quickly to keep up with the demands of the activity you're doing. Regularly getting your heart working a little harder in this way trains it to become more efficient, which can help reduce your risk for all sorts of cardiovascular problems. But you also don't want to be over-exercising, which can set you up for other health issues — even undoing some of the benefits of physical activity.
So knowing how hard you're really working can help you get the most out of that gym time. First, it's helpful to know your resting heart rate, which you can calculate by checking your pulse (try placing two fingers on your wrist or the side of your neck). Count the number of beats you feel in 15 seconds, then multiply that number by four, the Mayo Clinic says. This number is your resting heart rate, and, for most adults, it should be somewhere between 60 and 100 beats per minute. If you don't have a heart rate monitor, you can also use this method to check your heart rate when working out.
The second factor is your age. Once you have those numbers, the American Heart Association explains, you'll subtract your age from 220 to get your maximum heart rate. Then your target heart rate will be between 50% and 85% of that number. For instance, if you're 20, your estimated maximum heart rate will be 200, which would make your target heart rate between 100 and 170 beats per minute.
You can go a step further and take your resting heart rate into account (subtract your resting heart rate from your max heart rate, then multiply the result by 0.7 and 0.85 to find your target window). More detailed calculations also take your gender into account. But, for the average exerciser, the simple formula is enough to get the general idea.
These calculations are tried-and-true classics. But, as the American Council on Exercise (ACE) explains, recent research suggests it's not always the most accurate, possibly leading you to over- or under-train. That's why it's essential to pay attention to more than just your heart rate when working out; it's a helpful tool, but it's not everything.
The way you feel while exercising is just as important as the number on your heart rate monitor. And the way you feel may be very different from the way someone else feels, even if you're doing the same workout. So, if your body's telling you it needs to chill, you should absolutely feel free to dial it back or take a break — regardless of where your heart rate's at. Some other clues to pay attention to: how quickly and deeply you're breathing, how quickly you start sweating and how much you sweat, and whether or not you can carry on a conversation. If you feel like you're overdoing it — if you can't keep up your end of the RHONY convo, for instance — definitely take a second to slow it down.
Working with your doctor and an ACE-certified personal trainer can guide you to become more attuned to your body's signals and work up to your target heart rate safely. They can also help you adjust these calculations for any health issues or medications in your life, and they can suggest workout plans that gradually ease you into more strenuous exercise. With that, you and your heart will be even more ready to get back on the treadmill.