I’ve angered the elliptical machine. It wants to check my heart rate and repeatedly flashes its request on the digital display. I continue in oblivion. That is, until my new trainer notices. My sweat test, apparently, isn’t cutting it. I’ve been cardio coasting.

A lot of times, if you don’t monitor your heart rate, you won’t work out as hard as you could. (On the flip side, you might overdo it.) Measuring heart rate allows you to gauge your intensity, whether at the gym or on the trail. You can then optimize your routine, training at a high enough level to strengthen your cardiovascular system.

The science is straightforward. During exercise, our muscles need oxygen to help replenish the energy being burned. The heart must send a steady supply of O₂-laden blood their way. At your fittest, it takes fewer beats to get the job done. As we train, we actually turn the heart into a better pump. You’ll be able to do more. The muscles also become better at extracting oxygen.

Curious, I find myself placating the elliptical machine, using heart rate to boost my intensity. It’s not as confusing as I’d assumed. Within weeks, I can go longer without losing my breath. See for yourself with these simple tips.

IN THE ZONE  Heart rate is a measurement of cardiac activity, generally recorded in beats per minute. A healthy, resting heart rate is about 60 to 80 beats per minute. Maximum heart rate, meanwhile, describes the fastest pulse you can attain. To get a ballpark figure, subtract your age from 220.

Target heart rate—your exercise zone—represents 50 to 85 percent of that maximum. So for a 50-year-old, it’s 85 to 145 beats per minute (50 to 85 percent of 170). This is an estimate that doesn’t take factors like fitness level or health into account.

FEEL THE BEAT  Incorporate heart rate monitoring into your routine with interval training.  Alternate between the low and high ends of your target zone to vary intensity. For example, walk for four minutes then sprint for two. Over time, run for longer. It helps to build endurance. For the elliptical machine, choose the random program and increase the intensity level as you improve.

But this advice means nothing if you can’t check your heart rate. Doing it the old-fashioned way, place your middle and index fingers on your wrist. Record the number of beats in a 10-second period and multiply by six (15-, 30- and 60-second intervals work as well; multiply accordingly).

The drawback to this method: You have to stop to count. A heart rate monitor, starting at around $50, takes the guesswork out, relaying a real-time signal from a chest strap to a wrist receiver. It’s not gonna lie to you.

Modern elliptical machines will monitor your heart rate as you hold on to the handles.