Will Doing Workouts That Are Twice as Long Double Your Weight-Loss Results?

Summer is almost here, offering up the double-whammy of constant beach trips and weddings every other weekend. You know what that means: a renewed commitment to the gym because you want to look good and feel even better. In the interest of shaping up fast, should you lengthen your workouts for the best results? Actually, you should do the exact opposite and shorten them, says Debi Silber, M.S., R.D., W.H.C., F.D.N.

“We know so much more about fitness now," she says. "We used to think long, drawn-out cardio sessions were the best way to blast fat. Now we know the shorter bursts in high-intensity interval training burn so much more fat in a fraction of the time." Science backs her up in a major way: Not only does high-intensity interval training (HIIT) amp up your calorie burn, it strengthens your heart, helps regulate your blood sugar, and keeps your metabolism chugging along at a higher rate after the workout’s done.

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It seems logical that a longer workout would help you drop pounds faster, but there are a few reasons quick sweat sessions are the way to go. First of all, even though exercising pays off with feel-good endorphins, extended workouts can actually boost your levels of the stress hormone cortisol. “Your body perceives long workouts as a stressor, so your adrenal glands respond as if your body’s in crisis and flood you with cortisol,” says Silber. When your body interprets those stress signals, it doesn’t properly convert food into glycogen, or energy. Instead, it sends those calories straight to your middle, where they park themselves as fat, says SIlber.

Beyond that, longer workouts can promote an injury that sidelines you from the fitness game completely, especially if you’re jumping into them all of a sudden. “If you’re doing the same kind of exercise for a long time, you’re putting way too much stress and tension on your muscles, joints, and ligaments,” says Silber. HIIT workouts don’t leave you as injury-prone, and they give your muscles a chance to bounce back in their newer, sleeker forms.

RELATED: How Interval Training Is Different for Women

Longer workouts, on the other hand, might exhaust your muscles to the point where they can’t change as easily. “With the right kind of exercise, you’re breaking down the muscle in order to build it back up," says Silber. "When you over-exercise, you’re not giving your muscles a chance to repair." Ditching marathon workouts in favor of the HIIT variety helps promote muscle confusion, which protects your muscles from getting used to one kind of workout and not changing.

RELATED: 7 High-Intensity Workouts that Take 20 Minutes or LESS

Then there’s one of the biggest benefits of HIIT: It just takes less time. “The biggest excuse people make for not exercising is that they don’t have time," says Silber. "If you try to lengthen your workout, you just won’t want to do it." But you’ll be hard pressed to convince yourself you don’t have 20 minutes to squeeze in a workout, especially when you know it’s one that’s proven to deliver results.

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