High-Intensity Intervals Can Boost Metabolism

High-intensity workouts can sound intimidating, but one popular format combines bursts of energy with time to catch your breath.

Its formal name is high-intensity interval training or HIIT, with short periods to push your body with higher-impact moves followed by seconds of recovery, and studies indicate it can help boost metabolism and improve fitness.

At gyms, you might find the format by another name such as athletic training, cardio express or "insanity."

"High-intensity interval training means you're working pretty much as hard as you can for a set period of time, then there are drops in intensity; then you go back up," said Katrina Nebel, YMCA health and wellness director.

She teaches a cardio express class using the format.

Many HIIT workouts call for 60 seconds of exercise near the peak of a person's ability, then 30 seconds of easy activity - a pattern repeated - perhaps for a 30-minute workout. Other routines might have two minutes for a burst of energy, then 30 seconds of recovery, or even a one-to-one ratio.

CrossFit brings elements of high-intensity intervals such as hill sprints and carrying heavy loads. Another format is called Tabata, named for professor Izumi Tabata who studied the approach among Olympic speedskaters.

Nebel said Tabata often has sessions with 20 seconds of high intensity, then 10 seconds of recovery.

"You do that eight times to equal four minutes and then they have a minute recovery until you move to the next session," Nebel said. "That's one of the most popular right now. There are all different variations.

"Really, the way our energy system works is you can't work at that peak all the time, and that's why there's highs and lows as far as the intensity," Nebel added. "Essentially, the high-intensity part is where it raises the anaerobic threshold, when you're working hard."

Most people have heard the term "aerobic fitness," which means with oxygen, Nebel said. As WebMD puts it, aerobic exercise is "activity that strengthens the lungs and heart and improves your body's ability to use oxygen."

Anaerobic, meanwhile, is short bursts of exercise, typically strength based, according to Science Daily.

Nebel noted, "Anaerobic is going to be at that place when you go to say something to another person, and you're maybe getting out one or two words."

But what's intense for one person differs for another, said April Davis, a Washington State University Spokane clinical assistant professor. She's with the Department of Nutrition & Exercise Physiology.

Davis said somebody might be working at a maximum level doing only a partial jumping-jack.

"People might feel like there is no way they can get up and down on the floor and do burpees (squat, push-up moves), and that's what they picture as high-intensity," Davis said. "But they don't necessarily have to do that.

"While one person is doing full power jumps, another person might be tapping a foot out to the side and reaching up with one arm ... that might get their heart rate to their range. It's very individualized to the person's fitness level."

But for most people, maximum intensity requires "more of a jogging-type than a walking-type exercise," she said. "It could be squats with a little jump at the top of the movement, rather than a stationary squat, so you're adding a bit of power to get the heart rate up."

Some people use a calculation aimed at reaching 85 percent to 95 percent age-predicted maximum heart rate, which is 220 minus your age. So a 40-year-old person might work to a maximum heart rate of 180 beats per minute. The target is a little easier to gauge if you're wearing a watch or device that monitors heart rate.

"I'd say that's a big estimation, and it's not validated for older populations or people with chronic conditions, but it's the easiest way for us to come up with numbers," Davis added.

Today, people tend to listen to their bodies regarding what's high-intensity exercise through perceived exertion, such as that sign of getting only one or two words out between breaths.

Nebel said she's seen many fit people older than 50 who easily work at higher levels than age-related charts. "The formulas are very generalized; For most of us, our bodies are not generalized." YMCA group classes typically follow a perceived exertion curve during workouts because of too many variables of using heart-rate monitoring, she said.

"So if you're in my class and I want you to be at that interval place where you're working really hard, but you can have a whole conversation with me, then you're not there," Nebel added. "But if I ask you something and you just give me a nod, then I know you are.

"You ask people on a scale of one to 10, we are looking at being at an 8 or 9. Where are you feeling you are? Studies on that have shown that's very accurate. The first is a talk test, the other is just a perceived scale to see where people are."

While higher-intensity with intervals can be a fitness boost and done in relatively short workouts, Davis said standard exercise routines always hold their merit.

Continuous exercise from walking, cycling or swimming for 30 to 45-minutes can get the heart rate to 50 to 70 percent of your maximum heart rate, a moderate-intensity level offering health benefits.

But even a brisk walk at an incline or a dance-exercise class can reach closer to higher-intensity levels for some people.

High-intensity interval workouts also come with cautions, Nebel said, including that someone new to fitness or returning to workouts shouldn't start with HIIT routines because of injury risks. After you build strength and endurance, fitness instructors or trainers can help you do the workouts properly.

When you're there, Nebel suggests higher-intensity interval workouts about three times a week at a maximum around standard forms of exercise. Even regulars should watch for over-taxing the body and over-training, she added.

"That's where injuries can happen," Nebel said.

Contact the writer: (509) 459-5439, [email protected]

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