If you're anything like me, you don't really pay attention all those numbers on workout machines' display screens — except, maybe, the calorie count. But if you want to make sure you're pushing yourself, heart rate is just as important.

Your maximum heart rate — the amount you should avoid exceeding so you don't hurt yourself — is 220 minus your age. So, if you're 30, your maximum heart rate is 190. Your target heart rate [1] is 50 to 85 percent of this number, and if you're trying to lose weight [2], it's best to be on the higher end of this range. Cardiologist Dr. Nieca Goldberg, medical director of the Joan H. Tisch Center For Women's Health at NYU Langone Medical Center, recommends around 85 percent of 220 minus your age. But if that's too intense for you, 60 or 70 percent should also do the trick, says certified personal trainer Jamie Logie [3].

If you don't have a device that measures your heart rate, fear not: there are other ways to gauge how intense of a workout you're getting, says Logie. Pay attention to whether you're feeling warmer, breathing audibly, sweating, or licking your lips. These are all indicators that you're in the fat-burning zone. On the other hand, if you can't carry on a conversation, your workout may be too intense.

More important than any of these things, though, is how much you're exercising, says Goldberg. She recommends 45 minutes to an hour of exercise four to five times a week if you want to lose weight. "The longer you exercise, the more work you are doing, so you burn more calories and lose weight," she says.

Also of note: if your heart rate gets lower over time for the same intensity of exercise, that's actually a good thing, says Goldberg. "Heart rate is higher in people who are overweight or obese, and the heart rate goes down as they lose weight," she explains.

And remember, when it comes to your health, weight is just a small piece of the puzzle. There are plenty of other reasons to get your heart rate up [4], like making it easier for your muscles to use oxygen and move, preventing a variety of diseases, and even keeping your mind in top shape. So don't neglect your aerobic exercise, even if it's just a brisk walk.