Why you should try one of the hottest new workouts

Do you hate running or love it? Are you a weight-room regular or novice in need of guidance? New to the gym or a group-fitness fanatic? Increasingly, you'll see exercisers from all these groups exchanging sweaty high-fives in the very same type of workout class: one that combines high-intensity interval training (HIIT) on a treadmill and strength training on the floor.
These combination classes have been popping up on group fitness schedules of top gyms across the country, and for good reason. By alternating between sets of heart-pumping runs or sprints interspersed with a more catch-your-breath pace then hitting the floor for toning and strengthening moves, the classes leave even the fittest people fitter, faster, stronger and healthier, all while helping banish workout boredom, says Stephanie Fravel, an instructor certified through the American Council on Exercise who teaches Chicago Athletic Clubs' combo class, Strength & Stride.

Brief effort, far-reaching results
One reason hybrid classes like Strength & Stride are so effective is that they harness the power of high-intensity interval training. Research has found that HIIT nets all the perks of a long, steady cardio session — and possibly more — in a fraction of the time.

What to expect: After a warmup, you'll tackle treadmill segments that involve sprinting or running, often on an incline, for a brief interval — say, 30 seconds to three minutes, Fravel says. Then, you'll slow down your pace and spend about the same amount of time walking or jogging to recover.

Yes, it can be hard and the sprints can be a little uncomfortable, but reaching that intensity, even for a short period, is why it works. According to a recent 10-week study published in the journal PLOS ONE, high-intensity interval training helped one group of previously sedentary adults boost fitness, burn belly fat, improve cholesterol levels and reduce diabetes risk. Bonus: Participants also felt happier and healthier. Even better, they did it all working out less than an hour a week. In contrast, a control group who logged only moderate-intensity sessions needed to do more than two hours of sweating to see the same results.

The best of both worlds
Of course the HIIT portion comprises only half your time in class. Every 10 to 20 minutes, you'll hop off the treadmill and hit the floor for moves like squats, push-ups and medicine-ball training.

This is key for runners and other cardio junkies who tend to blow off strength training, which is essential for building and maintaining lean muscle and helping to injury-proof your bones and ligaments. It also fires up your metabolism for hours after you leave the gym. "A strong body is a healthier body," Fravel says. So these hybrid classes give cardio-lovers what they crave, but also force them to do some resistance training. And vice versa for those who prefer weight training. Think of it like putting cheese on your broccoli to coax you into eating veggies.

The alternating sprint-and-strength format also keeps your body and mind guessing, so muscles never adapt (read: you keep seeing results) and time flies by. With all this packed into a single 45-minute or hourlong session, it's no wonder the classes are speeding to the front of many fitness fanatics' agendas.

Make the most of your time
Don't let the idea of sprinting or the term "high-intensity interval training" intimidate you. "This can be a really hard class if you want it to be, but you can tailor it to any athletic experience," Fravel says. Here are her top tips for scoring the best workout:

Set your pace. Don't sweat it if you don't know your starting or sprint speed. Use the "talk test": When you're in the middle of a sprint you should feel out of breath and barely able to speak. During recoveries, aim to be able to carry on a conversation. Over time, your speeds will naturally increase — an easy way to track improving fitness.

Don't compare. The person next to you might be a marathon winner or someone who hasn't run since grade school. Race yourself, and don't let more experienced runners psyche you out. Instead, look to them for help, Fravel says. They were newbies once, too.

Push yourself, even if just a little. Fravel challenges students to try one thing in class they haven't done before, especially if it's scary. Try clicking up your speed during the last sprint or grabbing a heavier weight; the only way to get greater results is stretching your comfort zone.

Picture the finish line. When the going gets tough, envision someone or something you love or want waiting for you. "A yoga instructor once told me that you're either running from something or to something," Fravel says. "You'll feel better at the end of your workout when there's something you've been running toward."