Do you know what your resting heart rate is? If your answer is, “I leave that kind of thing up to my doctor!” you’re missing out on a vital piece of information about your overall level of fitness, as well as your cardiac health. Your heart rate is the number of times your heart beats (or contracts) in a minute. It’s measured in BPMs or beats per minute. You can measure your resting heart rate the old school way by “taking your pulse.” If you put two fingers on the inside of your wrist or side of your neck, you can feel the blood pulsing through blood vessels close to the skin’s surface. Each pulse counts as a beat. Or you can let a heart rate tracker do the job for you.

As its name implies, your resting heart rate is the amount of times your heart beats when you’re relaxed. This is an important number because it not only reveals how efficiently your heart pumps blood, but is a reflection of how fit you are. According to the National Institutes of Health, normal resting heart rate for children over ten and adults should be between 60 to100 BPM. Granted, that’s very wide range — in reality, it’s healthier to be on the lower end of the scale. In general, the more fit you are, the lower your resting heart rate. Some very fit athletes have resting heart rates as low as 40 BPM!

If you’ve started wearing an activity tracker and are embarking on an exercise program to improve your fitness level, tracking your resting heart rate is one way of measuring your progress. “Before you start a fitness program, it’s a good idea to measure your resting heart rate to get a baseline. Do it first thing in the morning. Then retest yourself about a month later. If your resting heart rate hasn’t come down, it could be a sign that you’re not training hard enough.” explains Aime Hoff, fitness consultant and personal trainer who is the founder of fitkit.com.

Your heart rate isn’t constant — it changes with activity so that your blood flow can keep up with your body’s demand for oxygen and other nutrients. For example, if you’re running on a treadmill, or sprinting to catch a train, your heart rate will spike to send more blood to your limbs. It’s not just physical exertion that can cause your heart to start pounding. Stress hormones can also cause a rapid rise in your heart rate. Your heart rate may also speed up if you’re dehydrated or have an infection.

Although fairly common and often benign, an irregular heartbeat may be a sign of cardiac or other health problems, especially if it’s accompanied by dizziness, chest pain, nausea or other unusual symptoms. Needless to say, if you experience any symptoms that don’t feel right, check with your health care professional.