HIIT Workouts Can Change Your Body on a Cellular Level

How this popular workout can lead to major changes in just a few minutes a day.

Here’s what to know about popular HIIT workouts. Getty Images

If you think you don’t have enough time to work out, you may be in luck.

Australian researchers found that just a few minutes of high-intensity exercise known as HIIT may be as good for your body’s cells as 30 minutes of moderate exercise.

That means you may no longer need to carve out an hour of your day just to reap the benefits of movement.

However, the study is small so there might need to be more research before doctors approve of two-minute daily workouts as a way to stay healthy.

The small study, which was published in American Journal of Physiology—Regulatory, Integrative and Comparative Physiology, looked at eight young adult volunteers and their cellular response to exercise.

The cells in your body tell scientists how truly beneficial exercise is, so while most people look for the benefits of exercise on the scale or in the mirror, scientists have to look inside your body.

In particular, they look at mitochondria, also known as the energy powerhouses of the cells.

Mitochondria are responsible for producing energy for your body. As you age, the production of energy from mitochondria slows, which is why older individuals have less energy than younger ones. Exercise creates new mitochondria, and it boosts the function of existing mitochondria.

A 2017 study found that maintaining healthy mitochondria is vitally important for defeating or holding back aging-related muscle problems, such as weakness and dysfunction.

This new small study examined mitochondrial changes after participants performed three types of exercise.

The first type required participants to exercise for 30 minutes at a moderate level.

The second type of exercise was modeled after the popular high-intensity interval training (HIIT) workouts. It required participants to perform five four-minute cycling sessions at near-maximum effort. Each session was separate by a one-minute period of rest.

The final type of exercise was designed as sprints: four 30-second cycling sessions at maximum effort. Each session was separated by 4.5 minutes of recovery time.

After each exercise, researchers looked at the amount of energy the participants spent on the workout. They then analyzed the mitochondrial changes to the cells in the participants’ thigh muscles.

What they found was that fewer minutes of a HIIT workout produced a similar response in mitochondrial function as longer moderate-intensity workouts.

“A total of only two minutes of sprint interval exercise was sufficient to elicit similar responses as 30 minutes of continuous moderate intensity aerobic exercise,” the researchers said in their study.

This study is small, so additional research is needed to see if the results hold on a larger sample size, but researchers hope this is a possible sign that exercise can be prescribed according to individual preferences, and that people can expect to still reap major metabolic benefits.

High-intensity interval training has been gaining popularity in recent years as the benefits of short, intense bursts of exercise become more broadly understood.

The HIIT workout has become increasingly popular as busy Americans continue to devote less time to physical well-being.

As a result, researchers and fitness experts are looking for ways to encourage people to give even small bits of their day to exercise and still reap rewards.

The HIIT style of exercise divides a workout into blocks, or intervals, of time. During some of the blocks, you’re doing exercise. During others, you’re resting.

What “high intensity” means, however, differs among fitness experts.

“When we say ‘high intensity’ we mean relative to you. If you’re just starting a training plan and have been inactive most of your life, that’s going to start off pretty slow,” said Joey Daoud, who runs the coaching company New Territory Fitness and is also a CrossFit level 2 coach. “For someone that’s been training consistently for a year or more, that’s going to look a lot faster. We’re just looking to get the heart rate elevated.”

The goal of HIIT workouts is to get your heart and your lungs working at peak capacity quickly in the sustained bursts of intense exercise.

“A true high-intensity interval is done at 90 percent of maximal heart capacity,” said Teresa Evans, a nationally-certified trainer and owner of T-Fit, Inc in Palm Harbor, Florida. “But not every person will push themselves there. In fact, if they did it right, they wouldn’t be able to do an hour-long HIIT class at their local gym.”

Evans says the goal is simply to push yourself to as high of an intensity as you feel you can handle at that time.

Kyra Williams, a National Academy of Sports Medicine–certified online personal trainer and nutrition expert, says the benefits of HIIT can be seen on your waistline and in your body.

HIIT increases “the amount of calories your body burns during and after your exercise session,” she said.

Plus, she added, “your metabolism tends to increase allowing you to use fat as fuel.” That means you burn more stored fat and may possibly lose weight or at least some body fat.

This latest study comes on the heels of a study that found HIIT workouts may be both beneficial in the ways Williams notes, and they may also be more fun.

A 2018 study asked 250 overweight or obese individuals to pick between HIIT-style workouts or conventional workouts. Less than half (42 percent) chose the fast-paced but abbreviated HIIT workouts.

After 12 months, researchers found there was no difference between exercise groups in weight. However, HIIT participants reported greater enjoyment of the physical activity they had chosen.

What’s more, though many of the study’s participants had dropped out by the 12-month mark, those who did remain saw more significant reductions in both weight and visceral fat.

“If you only have 20 minutes to work out this is definitely the most effective way to spend it,” Williams said.

Despite its popularity, HIIT isn’t for everyone, and it’s certainly not something you should do daily.

“If you have any cardio problems or health concerns this may not be for you,” Williams said. “Also, I suggest someone just starting a workout routine not focus on HIIT immediately. Before worrying about getting someone’s heart rate above 70 percent then bringing it back down to go back up again, that person needs to have the endurance to handle cardio for 20 minutes.”

Greg Pignataro, a Certified Strength and Conditioning Specialist (CSCS) and personal trainer with Grindset Fitness in Phoenix, Arizona, suggests you combine HIIT with other types of exercise for maximum results.

“For fat loss and muscle gain, which 90 percent-plus of people want, HIIT plus a resistance training or weightlifting program is the Holy Grail,” he said. “This combination will maximize your body recomposition efforts, and when paired with appropriate recovery and nutrition, will almost inevitably lead to a decrease in body fat and an increase in muscle mass.”

Cat Kom is the founder and lead trainer at Studio SWEAT and Studio SWEAT onDemand. She says HIIT is a great workout, too, but people new to the style of fitness need to pace themselves.

“Any workout is better than not working out at all yes, but oftentimes this high intensity for a short period of time can lead to higher risk than result,” she said. “Injuries are more common when you’re HIITing it hard. So, if you aren’t in a normal routine or you’ve taken time off, and all of a sudden you hit it hard, you have a higher risk of getting hurt. You can’t just go from zero to hero, or five days a week hard core. It’s a recipe for failure. You’re going to burn out.”

Australian researchers found that just a few minutes of high-intensity exercise known as HIIT may be as good for your body’s cells as 30 minutes of moderate exercise.

Experts caution that study is small so there might need to be more research before doctors approve of two-minute daily workouts as a way to stay healthy.

Fitness experts also caution that people who want to start a new HIIT regimen should go slow and work with the professionals so they don’t injure themselves.

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