HIIT (high-intensity interval training) has been the most buzzed-about sweat method for a while, but there's a new approach gaining momentum: LISS, or low-intensity, steady-state cardio. OK, it's not really new (hello, elliptical!). So why the sudden spotlight?

"People are burned out; they're fed up with always pushing to their limits," explains Joe Holder, a Nike running and training coach and a performance training at S10 in New York City. "LISS is a less intense alternative that allows you to decompress while offering full health perks."

You don't need to pick one or the other, adds Anna Victoria, a certified NASM trainer and creator of the Fit Body Guide regimen: "It's about alternating between the two and taking advantage of the fat-burn benefits of all heart-rate training zones," she says.

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Here's the essential info on both practices:

LISS

What it is: Cardio performed at a low to moderate intensity—50 to 65 percent of your max heart rate—for a minimum of 45 minutes. Think jogging, swimming, biking to work, or going for a brisk walk. 

Benefits: The relaxed pace of this training method is easier on the joints, helps lower your resting heart rate, and is a great stepping stone for those looking to increase their intensity.

The downsides: Not only is it time-consuming, but as your body adapts, you'll have to up your exercise time to continue to see changes. And it won't boost your muscle mass or strength.

Burn potential: A 150-pound woman can expect to crush about 350 calories in 45 minutes.

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HIIT

What it is: A cardio interval technique in which you alternate 20- to 30-second bursts of all-out intense effort (80 to 90 percent of max heart rate) with recovery periods.

Benefits: You don't have to spend massive amounts of time getting sweaty, and you'll rev your ticker, recruit more muscles, and burn calories even after you've stopped.

The downsides: You can't really reap the benefits of HIIT without an aerobic base. Translation: You still need to get your LISS on. And it may not be safe if you're unfit.

Burn potential: A 150-pound woman can torch roughly 190 calories in 20 minutes.