High-intensity interval training is one of the biggest trends in fitness, but it has always seemed a bit scary to me. To a mere mortal with achy knees and an aging body, even the acronym — H.I.I.T. — sounded intimidating.

But recently, I overcame my fears of intense interval training, which involves bursts of all-out exercise followed by brief periods of rest. When it was all over, not only did I feel great, but to my surprise, I enjoyed it.

And a wave of scientific evidence suggests that H.I.I.T. workouts are exactly the type of exercise a middle-aged, out-of-shape body should be doing. Research has shown that H.I.I.T. workouts are the best exercise at any age, and for older people especially, it’s the most efficient way to exercise and reverse the signs of aging within cells. It’s also faster and more interesting than the hourlong slogs on the treadmill that many of us think we should be doing (but often don’t.)

So how did I overcome my fears about high-intensity training?

It began with a heart rate monitor. Alex Chriest, a fitness coach at the Johnson & Johnson Human Performance Institute in Orlando, showed me how using a heart rate monitor could make high-intensity exercise not only easier, but more fun.