As one of the most popular exercise trends for more than a decade, high-intensity interval training (HIIT) clearly offers some benefits. These workouts aren’t just a time-efficient way to boost your fitness. Research shows that HIIT can improve key measures of cardiovascular health for all kinds of people, including those recovering from heart attacks or heart surgery. Another benefit: high-intensity effort, even for just short bursts, can trigger the release of mood-enhancing brain chemicals.
As the name suggests, HIIT features high intensity (vigorous) activity performed in intervals (short periods of time) with short periods of either rest or lower intensity activity in between. During bursts of vigorous exercise, your heart rate rises higher and then stays higher than it would normally be between these high-intensity bouts. Compared to 20 minutes of moderate-intensity exercise, a 20-minute HIIT session will burn more calories, strengthen your heart more, and help your body use oxygen more efficiently.
“If your goal is to improve your fitness, moderate intensity exercise certainly works. But HIIT training can raise your fitness level faster in less time,” says Dr. Sawalla Guseh, director of the Cardiovascular Performance Program at Harvard-affiliated Massachusetts General Hospital. As he points out, if you do mostly vigorous exercise, you can meet the federal exercise guidelines in just 75 minutes a week, while doing most moderate exercise takes twice as long (150 minutes a week).
Prefer HIIT?
If long sessions of vigorous exercise feel too challenging, adding some HIIT training to your workout routine can be a happy medium. Even short breaks of high-intensity exercise appear to trigger the release of endorphins—the brain’s “feel good” chemicals. “In our clinic, we definitely see patients who say that HIIT training brings them the most joy,” says Dr. Guseh. In addition, endorphins can counteract pain, which can mitigate some of the discomfort that can occur during HIIT workouts, so people perceive them as more pleasant than expected.
Still, the most important thing is to find a form of exercise that you enjoy and can do consistently in the long run, says Dr. Guseh. Regular moderate-intensity exercise is also a great way to keep your cardiovascular system healthy.
Get started with HIIT
If you have heart disease or are at increased risk for it, be sure to check with your doctor before adding high-intensity exercise to your routine. People at increased risk include those with two or more of the following: diabetes, high blood pressure, high cholesterol, or a family history of heart disease.
To reach the right intensity
Traditionally, HIIT features 30 to 90 seconds of high-intensity effort followed by an equal or longer period of lower-intensity activity or rest. High intensity is often defined as reaching 85% of your maximum heart rate (see “All About Your Heart Rate” in June 2023 Heart letter). A simpler option is to aim for an “8” on your personal perceived exertion scale (where 1 is very easy and 10 is as hard as you can possibly go).
When first starting out, alternate a few short intervals of high-intensity exercise with longer periods of moderate or light exercise. Say you usually walk for 30 minutes at a time. Start by walking for five minutes. Then walk as fast as you can or jog for one minute. Go back to your usual pace, or even a little slower, for three minutes. Repeat the fast walk – slower walk five more times. Once you get fitter (or if you’re in reasonably good shape), you can spend more time walking faster or jogging and less time walking around or resting.
You can turn any cardio workout—cycling, swimming, elliptical, stationary bike, treadmill, stair climber, rowing machine, and even dancing—into an interval session. The easiest way is to simply speed up and slow down. Outdoors, you can add hills to a running or cycling route to create more intensity. Indoors, you can add some stair climbing or jumping. For variety, try other HIIT variations (see “Internationally Inspired Interval Training”). Harvard Health Publishing’s report Interval trainingcontains five sample workouts, including warm-ups and stretches.
Internationally inspired interval training
Try one of these HIIT variations to add fun and challenge to your workout.
Fart game. Swedish for “fartlek”, fartlek is a more relaxed, fun way to do intervals. You don’t have to worry about distance, time or heart rate. Instead, you push yourself as long as you can based on how you feel, or until you reach a goal like a tree, light pole, house, or someone in front of you. Then you will recover as long as you need to. Your intervals do not have to be identical. When you feel ready, pick another goal and go. Although the intervals are informal, they can still be challenging.
Tabata. Named after the Japanese scientist who created it, Tabata workouts feature 20-second work intervals and 10-second recovery intervals performed eight times in a four-minute set. Try it with any type of aerobic exercise, such as walking, running or cycling. Tabata classes often include several rounds of different exercises, such as jumping jacks, knee pulls or mountain climbers, designed to work all the major muscle groups. Instructors combine different variations of the four-minute series to create workouts that last half an hour to an hour.
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