When it comes to working out, longer isn’t always better.

Wait, what?

Believe it or not, there is quite a bit of (comforting) research supporting shorter, more intense workouts—for both performance and health benefits, including weight loss, Pete McCall, a personal trainer and author of Smarter Workouts: The Science of Exercise Made Simple, tells Health.

While high-intensity interval training (HIIT) is not new—interval training has been around for decades—there is a recent surge in using this approach for fitness and weight loss.

“In the last 20 years, HIIT has been studied for its effects on boosting performance and its high caloric burn,” McCall says.

When it comes to HIIT being a better workout for caloric burn, McCall gives this analogy: HIIT is city driving, while longer, slower workouts are highway driving—and calories are your gas.

“With city driving, you’re starting and stopping a lot, and you’re burning more gas,” he says. “On the highway, you’re maintaining a steady pace and you’re much more efficient.”

So how do you choose the best HIIT workout? The bottom line, McCall says, is to not make your working intervals too long and your rest intervals too short.

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What to look for in a HIIT workout routine

If you find a HIIT workout that’s 45 minutes, run away. It’s way too long, McCall says.

“The biggest mistake people make is thinking a 45-minute HIIT workout is great. But it should be 15 to 20 minutes,” he says.

In fact, you can reap benefits from just four, yes, four minutes. McCall cites the popular, effective Tabata method, which is a four-minute workout: You work at your max capacity intensity for 20 seconds, rest for 10 seconds, and repeat eight times.

“Four minutes doesn’t sound like a lot, but if you’re doing it right, that last minute really sucks,” McCall says. “When it comes to high intensity, less is more.”

If your work intervals are longer than 30 seconds, you’ll run out of energy and be unable to complete the workout. Alternatively, if your rest intervals are too short, your body won’t have enough time to recharge for the next work period.

McCall also cautions against doing more than two HIIT workouts a week. Your body needs about 48 hours to recover from the wear and tear, he says.

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Why does HIIT burn more calories?

The short answer is it takes energy to burn energy. When you push your body really hard for 20 or 30 seconds, you’re expending a ton of energy, McCall explains. And during your recovery interval your body is taking the byproduct of that burn—lactic acid—and turning it back into energy your muscles can use, called ATP.

When you exercise for longer periods of time at a lower intensity, you still expend energy—but not as much as during that high-intensity burst.

That said, people tend to think they burned more calories than they did, leading to overeating and weight gain, McCall says. The sustained calorie-burn from a HIIT workout, for example, is about 100 to 200 calories, which is not insignificant. But a post-workout Starbucks muffin is about 400 calories.

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Try these HIIT workouts

McCall has two go-to HIIT workouts he recommends.

Lateral ice skaters

Stand with your feet hip-width apart.

Step your right foot to the right, then step your left foot to the right. Repeat the motion to the left side. Continue to repeat the motion for 30 seconds at a comfortable pace.

Then, increase your effort for 20 seconds. Repeat the motion like you’re ice-skating.

Finally, increase your effort for 10 seconds of explosive movement, like you’re speed-skating.

Repeat this entire sequence for five to seven minutes.

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Copenhagen protocol

McCall recommends following this routine on a bike, rower, or self-powered treadmill. (While it can be done on a normal treadmill, it takes precious time to adjust the speed, he says.)

Warm up for five minutes.

Move easy for 30 seconds; your feeling of effort should be about a five on a scale of one to 10.

Move hard for 20 seconds, about an eight on a scale of one to 10.

Move as hard as possible for 10 seconds.

Repeat the entire cycle for five minutes and then cool down.

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