HIIT Workouts Are So Good for You—Here's How to Work Them Into Your Exercise Routine

HIIT was named one of the top 10 fitness trends of 2021 by the American College of Sports Medicine. But what exactly is it? Here’s everything to know about this type of exercise.

High-intensity interval training (HIIT) continues to be a beloved type of workout among fitness enthusiasts. Numerous reasons account for its popularity, and given its health benefits, it's worth adding to your own fitness routine, too. Here's the lowdown on HIIT so you can cash in on its advantages.

What exactly is HIIT?

HIIT—which stands for high-intensity interval training—is, simply put, a type of workout that alternates between hard (high-intensity) and easy work. "During this workout, you spike the heart rate to near max levels of exertion (70 to 90 percent of max heart rate) followed by a brief period of activity recovery (55 to 65 percent max heart rate) or complete rest," says Mike Donavanik, certified strength and conditioning specialist and celebrity trainer in Los Angeles, and the founder and CEO of Sweat Factor.

After a short warm-up, you cycle through this pattern for the duration of your workout, which might last 20 to 45 minutes—although 20 to 30 minutes is the sweet spot. You'll see 45- to 60-minute HIIT workouts, but these are structured to allow for extra recovery time throughout. "A rule of thumb is the harder the intensity, the shorter the workout," Donavanik says. You can do HIIT, by the way, solely with cardio, just resistance training, or both.

Why HIIT is so good for you

While this may not exactly sound like the most fun workout, it does come with a long list of pay-offs. For starters, it's an extremely efficient type of exercise. "A HIIT workout leads to higher calorie burn in far less time than steady-state cardio and/or traditional strength training," Donavanik says, which means you get more health benefits in a shorter amount of time.

It's also a fantastic way to build your cardiovascular fitness in a short amount of time, says Mike Matthews, certified personal trainer in Clearwater, Fla., founder of Legion Athletics and author of Bigger, Leaner, Stronger. He points to a study conducted by researchers at McMaster University who found that just three HIIT workouts a week for two weeks—a total of 15 minutes of actual intense intervals—was enough to show marked improvements in endurance and enzymes responsible for powering muscle contraction.

But there's another unexpected plus to doing HIIT workouts. "It pushes you out of your comfort zone and improves your resilience, which has positive downstream effects on every area of your life," Matthews says, adding that traditional cardio doesn't hold a candle to HIIT when it comes to building grit.

Can anyone do HIIT?

While HIIT is often used by elite-level athletes, it's a form of exercise that absolutely anybody at any fitness level can start doing and benefit from. "Studies have shown that HIIT is well-tolerated in people with heart disease, diabetes, obesity, and in cancer survivors," Matthews says. Of course, you should always talk with your doctor before you start any type of intense exercise, but you may be surprised how well your body tolerates HIIT.

That said, if you've been sedentary and are just starting an exercise program, you'll want to build your way up to doing serious HIIT workouts. Begin by doing regular, low-intensity cardio (brisk walking, light biking, swimming, low-impact workouts) to prepare your body for the physical demands of HIIT, Matthews says. Then once you've done this for a few weeks, you can start doing HIIT.

Matthews notes that if your primary activity is running, and you want to try HIIT, one tip is to start HIIT on an exercise bike versus running, at least in the beginning. "If you aren't used to running, doing it in the form of HIIT will take a toll on your body and make it hard to recover from your workouts," Matthews says. And for some, doing high-intensity intervals while running can also be hard on the knees, ankles, and hips.

HIIT tips for getting started

There are various ways to do HIIT, but Donavanik likes using a one-to-one work-to-rest ratio when doing cardio like running, walking, or cycling. That means you'll engage in high-intensity movement for a certain amount of time, followed by a period of rest for the same amount of time.

For instance, you might do 40 seconds of sprinting, high-resistance/speed biking, or speed walking, followed by a 40-second recovery break, then repeat this cycle (40 seconds of high-intensity effort, 40 seconds of rest).

To make things more challenging, you can also try a two-to-one work-to-rest ratio, where you go hard for 40 seconds and then take an active recovery for only 20 seconds (then repeat).

If you're doing more strength training with multiple exercises, Donavanik says the format changes a bit to become a HIIT circuit. Instead of doing one exercise for two or three sets, resting, and then moving onto the next exercise, you'll want to do three to four exercises back to back with minimal to no rest in between. You'll then give yourself a longer, 30- to 90-second break before repeating the entire circuit.

Want to combine cardio and strength training for a tough HIIT circuit? For example, start with 10 push-ups, move directly into 20 bicep curls, follow with a 30-second sprint or 30 seconds of mountain climbers, then finish with a recovery break, Donavanik says.

The main thing when doing HIIT is to make sure that when you're doing the hard-work efforts, you're working really hard. You want to make each period of effort truly count and feel like you deserve each rest. As Donavanik says, "for HIIT to truly work, you have to push your limits." And if you see your form starting to deteriorate, either stop the workout or give yourself longer rest periods.

How often you should do HIIT depends on your fitness goals, but for general fitness gains, aim for up to three sessions a week, spreading them out on non-consecutive days.

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