February 13, 2020

What is high-intensity interval training?

Madison, Wis. — If there are any fitness fanatics in your life, chances are you’ve heard one of them mention HIIT over the past year or two.

HIIT, an acronym for high-intensity interval training, is among the fastest-growing trends in exercise, embraced by serious athletes and ordinary people alike. But unlike yoga, spinning or other current fitness crazes, HIIT is not a specific activity. Instead, it’s a method of managing the vigor of a workout that can be applied to many different activities and tailored for people of all fitness levels.

It’s that flexibility paired with shorter workout durations that makes HIIT appealing to many people, says Kate Hemesath, a fitness supervisor with UW Health's Sports Medicine Fitness Center.

“The big thing about HIIT training is that it produces the same or similar results (as low-intensity steady-state exercise) but in a shorter amount of time,” Hemesath said, adding that effective HIIT workouts can be as short as 30 to 45 minutes.

As the name implies, HIIT workouts consist of brief intervals of intense effort, followed by recovery periods. The American College of Sports Medicine defines “high-intensity” as durations where an activity is performed at 80 to 95 percent of a person’s estimated maximum heart rate. The length of those high-intensity intervals, however, is entirely adaptable to a person’s fitness level and can range anywhere from a matter of seconds to several minutes or more.

HIIT workouts have been associated with numerous health benefits, including lowering blood pressure and resting heart rate.

Hemesath says HIIT is especially beneficial for weight loss because studies have shown it improves insulin sensitivity and spikes two key hormones – epinephrine and norepinephrine –that, together, help break down fat.

HIIT also has a greater post-workout effect on metabolism than steady-state exercise, keeping metabolism elevated for several hours as the body works to restore itself. According to the American College of Sports Medicine, HIIT workouts expend anywhere from 6 to 15 percent more calories through post-workout burn.

“By producing a higher and longer post-exercise caloric burn, you’ll be burning these additional calories without any extra effort!” Hemesath said.

HIIT Taking Hold

The effectiveness of HIIT in improving health has been noticed.

Across the country, fitness studios dedicated to HIIT training have cropped up and experienced tremendous popularity. Many of those studios pair activities like treadmill walking or running with weight training and real-time heart rate monitoring, which enables members to closely monitor their effort over the course of the workout.

But for people who prefer to incorporate HIIT into their own activity -- whether that’s walking, running, biking or swimming -- Hemesath says using a perceived exertion scale can be just as effective.

“One of the biggest obstacles to exercise is finding equipment or time,” Hemesath said. “Unlike some fitness trends, I think HIIT will be here to stay because it’s so adaptable.

“It can be as simple as walking around a track at varying intervals, but you can also plug in different exercises very easily depending on what you want to do.”

Too much intensity right away can be detrimental, especially for someone new to exercises, so Hemesath suggests consulting a physician before starting any HIIT program.

“Fitting in some form of movement each day is good for both your mental and physical health,” Hemesath said. “The incorporation of HIIT into a basic conditioning program will optimize the numerous health benefits of exercise in a fun and efficient way.”