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HIIT Workouts May Be Best Way to Optimize Body Composition

High-intensity interval training helps build lean muscle and trim belly fat.

High-intensity interval training (HIIT) is a tried-and-true method for achieving peak cardiovascular fitness and burning body fat. During a structured HIIT workout, short bursts of high-intensity “anaerobic” physical activity are followed by a recovery period of much lower-intensity aerobic exercise. This cycle is repeated multiple times and followed by a cool down.

Monika Olszewska/Shutterstock
Source: Monika Olszewska/Shutterstock

Recent research from the Mayo Clinic monitored the outcome of 120 cardiac rehabilitation patients who did HIIT workouts compared to a control group that only performed moderate-intensity continuous training without intervals. The researchers found that HIIT workouts resulted in building more lean muscle mass, losing more body fat, and trimming about an inch more from waistline measurements.

The findings of this pioneering study, “Effect of High-Intensity Interval Training on Total and Abdominal Fat Mass in Outpatient Cardiac Rehabilitation Patients with Myocardial Infarction,” will be presented later this month at the American College of Cardiology's 68th Annual Scientific Session (March 16-18, 2019) in New Orleans.

According to a press release, this is the first study to investigate the impact of HIIT workouts on body composition and fat distribution in patients with a history of cardiovascular disease.

"A considerable amount of research on HIIT has been done in athletes to demonstrate its ability to improve total exercise capacity and sports performance," the study's lead author, Yaoshan Dun, said in a statement. "Scientists and clinicians are just beginning to recognize the power that HIIT may have in clinical populations to prevent a second heart attack in patients who've already had one."

Dun is a cardiac rehabilitation specialist at the Mayo Clinic in Minnesota and is also affiliated with the Xiangya Hospital of Central South University in Changsha, China.

During the first stage of this study, on the effects of HIIT training compared to steady-state cardio at moderate intensity, Dun and colleagues at the Mayo Clinic assessed the cardio-respiratory fitness of ten-dozen volunteers. After determining which patients were physically capable of high-intensity exercise, they offered 90 people the opportunity to try HIIT. The other 30 people in the study were prescribed moderate-intensity continuous training without high-intensity bursts. Both groups worked out three times a week for 12 weeks.

Those in the HIIT group alternated between a one-minute burst of high-intensity exertion (e.g., stationary bicycling at a pace that made it impossible to converse in full sentences) followed by a three- to five-minute recovery period of low-intensity exercise (e.g., biking at a pace where having a conversation was easy). This HIIT cycle was repeated between four to eight times during each workout session.

Those in the steady-state cardio group performed 30 minutes of continuous moderate-intensity physical activity at an individualized “Goldilocks” exertion level that wasn’t too light and wasn’t too vigorous for that person. During moderate-intensity aerobic exercise, speaking in short sentences is easy, but it would be tough to recite a Shakespearean soliloquy without becoming breathless.

Notably, after 12 weeks of sticking to each of these exercise regimens, the researchers found that those in the HIIT group lost an average of 4 pounds of body fat and gained about a 1.5 pounds of lean muscle mass. On average, they also trimmed about one inch more from waist circumference than those who only performed moderate-intensity exercise.

Interestingly, when gauged only by changes in body weight or standard body mass index (BMI) charts, there wasn't any noticeable difference between the two groups. This is because the gain of lean muscle mass (which weighs more than body fat) threw off the metrics. Most importantly, because the HIIT group trimmed more belly fat, the researchers speculate that HIIT study participants probably reaped more heart-health benefits.

“Carrying more fat around the abdomen is associated with the greatest risk [of heart disease]. The lack of a significant difference between the two groups in terms of total body weight or BMI is likely related to the fact that participants performing HIIT gained muscle while losing fat,” Dun said.

Another study by Dun and colleagues compared HIIT workouts to moderate-intensity physical activity in patients with metabolic syndrome undergoing cardiac rehabilitation. This research also showed that HIIT reduced more belly fat. But again, these findings might have been overlooked because total body weight loss and BMI were comparable to those who did continuous moderate-intensity exercise without high-intensity intervals.

"These findings support the use of HIIT as an essential treatment tool to improve body composition in heart attack patients enrolled in early outpatient cardiac rehabilitation. Our data suggest that, compared to moderate-intensity continuous training, supervised HIIT results in greater improvement in these patients," Dun concluded. "HIIT may contribute to better outcomes for patients with abdominal obesity who have cardiovascular risk factors or established heart disease."

HIIT + HIIPA = A Winning High-Intensity Combo

Last month, another international consortium of exercise physiologists and public health advocates introduced a new acronym into the lexicon of workout jargon called “HIIPA.” This five-letter acronym stands for “high-intensity incidental physical activity.”

HIIPA represents everyday choices people can make that cause someone to “huff and puff” for .5 to 2 minutes as he or she goes through the motions of day-to-day life in street clothes. HIIPA includes activities such as taking the stairs instead of an escalator or elevator, raking leaves, shoveling snow, getting up from your desk to dance for a minute or two when a favorite song comes on the radio, etc.

The impetus for giving HIIPA a name is to raise awareness that—in addition to making structured HIIT workouts a part of one’s gym routine or outdoor exercise regimen—everybody who's on the go can reap the benefits of high-intensity exercise in short bursts throughout the day.

Prescriptive advice: One easy way to create a fail-proof HIIPA habit is to make a deal with yourself that you always take the stairs “going up” in a subway station, office building, shopping mall, airport... but give yourself a pass to take the escalator or elevator “going down.”

Based on mountains of empirical evidence, my advice as a coach is to structure weekly routines that mix-it-up in terms of continually blending MVPA, HIIT, and HIIPA. For example, in a perfect world—someone with the time, energy, physical ability, and self-motivation—could do 30-60 minutes of moderate-to-vigorous physical activity (MVPA) three days a week, high-intensity interval training (HIIT) at least twice a week, and consciously seek short bursts of HIIPA throughout the day.

As always: Please use common sense and consult with your primary care physician before beginning any new physical activity or kickstarting a vigorous exercise regimen—especially if you have not done any high-intensity physical activity recently.


Yaoshan Dun will present the study, "Effect of High-Intensity Interval Training on Total and Abdominal Fat Mass in Outpatient Cardiac Rehabilitation Patients with Myocardial Infarction," on Sunday, March 17, at the American College of Cardiology's 68th Annual Scientific Session in New Orleans.

Emmanuel Stamatakis, Nathan A Johnson, Lauren Powell, Mark Hamer, Vegar Rangul, Andreas Holtermann. "Short and Sporadic Bouts in the 2018 Us Physical Activity Guidelines: Is High-Intensity Incidental Physical Activity the New HIIT?" British Journal of Sports Medicine (First published online: February 20, 2019) DOI: 10.1136/bjsports-2018-100397

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