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No other fitness trend has made the same bang as HIIT—high-intensity interval training. Classes like CrossFit and SoulCycle mix short bursts of all-out activity with a quick recovery breather. But this isn't the only way to get moving. Enter the HIIT vs LISS debate. HIIT's low-key cousin LISS, or low-intensity steady-state, is a more relaxed, single-pace workout session you do for longer, like a half-hour jog. "They each have their own benefits, so ideally, you'll try a combo of both," says Pete McCall, an exercise physiologist and spokesperson for the American Council on Exercise. "But ultimately it's about which one you enjoy more and will do." Here, some of the payoffs of each type of exercise.
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Both workout styles can help reduce body fat, but you'll see results in less time with high-intensity workouts. In about 10 weeks, HIITers burned as much fat through 90 minutes of total exercise a week compared to those who did LISS and worked out for two and a half hours, according to a study in Obesity Reviews.
Two weeks of HIIT can improve insulin function (the hormone that regulates blood sugar). LISS helps too, but it'll take about twice as long before you see a benefit, found research published in the Scandinavian Journal of Medicine & Science in Sports.
According to a study from the International Journal of Environmental Research and Public Health, compared to continuous training, HIIT leads to a more resilient ticker that easily speeds up and winds down based on high or low stress (called heart rate variability), kind of like the automatic transmission in your car. Less variation in heartbeat speed means sticky gears that don't shift well, which may lead to heart disease.
Just 20 minutes of HIIT revs your metabolism, helping your body burn nearly 200 extra calories after you leave the gym, found a study in the journal Sports Medicine Open.
LISS burns more calories during your workout, found a study in the Journal of Sports Science and Medicine. Plus, its comfortable pace may mean you can exercise longer.
There may be an upper limit to the perks of super-intense workouts. In a study published in the Journal of the American College of Cardiology, joggers running about a 12-minute mile had a 78 percent lower risk of premature death, a benefit that sprinters didn't see.
Especially if you're in less than tip-top shape. "If you work out too hard, too quickly, your body may not be ready to take on HIIT training," says McCall. "Low-intensity exercise helps prepare your body." (And, he notes, doing more than three HIIT workouts a week—even if your body is up for it—could lead to injury.)
Some have a need for speed, but researchers found that previously sedentary adults preferred LISS, per their study in the Journal of Sports Science and Medicine.
Movement is good for your body and there certainly isn't a best workout for everyone. Whether you want to go for a walk, hit the gym, hold a kitchen dance party or head to a yoga class, it's important to listen to your body and figue our what works for you.