What if your workout gave your body exactly what it needed? And what if you could clearly measure the results, and even get instant feedback?

Well, you’d probably get better, faster.

You can do all that—including the “get better, faster” part—with heart rate interval training, says Alwyn Cosgrove, co-owner of Results Fitness in Santa Clarita, California and top Men’s Health fitness adviser.

Here’s how it works: Instead of pre-determining how long you work and rest for a particular exercise—for example, “work for 40 seconds, then rest for 20 seconds, and repeat”—you let your heart rate tell you how long you do each.

“I work until my heart reaches 85 percent of max, and then rest until it reaches 65 percent of max,” says Cosgrove. You’ll need a heart rate monitor, of course. “Just have it ‘beep” at the high and low limits,” he says.

Cosgrove likes to rotate between four exercises—for example, jump rope, kettlebell swings, battling ropes, and sled pushes—but you could choose do more movements, or fewer. “I do the first exercise until I hit the heart rate I’m looking for, and then I let myself recover until it’s back down to 65 percent,” he says. “Then I move on to the next exercise.”

Cosgrove uses that approach with all four exercises, and then repeats the process for as many rounds as he can complete in a given time period—say, 30 minutes.

“The cool part is that the periodization is built in. As my fitness improves, I recover faster between exercises and do more rounds,” says Cosgrove.

“If I’m tired or just got off a plane, my heart reflects that—so I don’t get as many rounds completed. It takes all the guesswork out of the session.”

Ever feel tired and wonder if you should dial your workout back? Or on the flipside, feel so great that you want to exercise harder than usual? Heart rate interval training adjusts your workout automatically. If you follow Cosgrove’s advice, your body will dictate how much rest you take and how many rounds you complete.

Cosgrove points out that you could use just about any exercise. “Some exercises don’t jump the heart rate up fast, so you just end up doing a longer interval,” he says. “Shuttle runs are always good, stepups work, and bikes, rowers, and other forms of traditional cardio are effective, too.”