Scientists Reveal 1 Exercise That Burns Fat and Maintains Muscle

All exercise is good exercise, as long as you do it with proper form. But depending on the results you want to achieve—whether it’s incorporating more movement into your day, building strength, or reducing fat—some exercise types may prove more beneficial than others. In fact, scientists have uncovered one type of exercise in particular that may have a key advantage when it comes to losing fat while still preserving valuable muscle mass, especially for older adults.

Meet the experts: Karena Wu, D.P.T., board-certified clinical specialist in orthopedic physical therapy and owner of ActiveCare Physical Therapy; Anna Di, D.C., C.E.S., corrective exercise specialist, chiropractor, and owner of UNITY Chiropractic Wellness in New York City.

That’s the key takeaway from a recent study published in Maturitas, which set out to determine which type of exercise most effectively reduces body fat without reducing muscle mass in turn. The participants included 123 older adults with an average age of 72 and no preexisting medical conditions, whom the researchers split into three groups. One group received a low-impact exercise program, one received a medium-intensity program, and one received a high-intensity interval training (HIIT) program.

After each group completed three supervised 45-minute exercise sessions a week for six months and the researchers analyzed the changes in the participants’ body composition via scans taken at the start and end of the study period, the results were clear. While both the HIIT program and the moderate-intensity program were effective at reducing body fat, the moderate-intensity program also resulted in subtle muscle decline. Only the HIIT workout was effective at both reducing fat and maintaining muscle.

Before you throw your current workout plan out the window, what does that actually mean for you? Fitness experts break it down below.

Why might HIIT exercise reduce fat without reducing muscle?

Before we get into the HIIT exercise benefits the researchers found, what actually is HIIT? “High-intensity interval training is a type of exercise training that incorporates high-intensity cardiovascular intervals with active recovery built in between,” explains Karena Wu, D.P.T., board-certified clinical specialist in orthopedic physical therapy and owner of ActiveCare Physical Therapy. “This exercise training allows the body to recover before performing activities that require a lot of energy expenditure.”

In this particular study, the HIIT exercise intervention was performed on a treadmill, but it can include other whole-body exercises like strength or resistance training. The key component is the interval structure. “Interval training reinforces active recovery for the body to optimize peak performance in both strength training and fat burning. The extremely high-intensity exercises will recruit more muscle fibers to help with muscle mass maintenance,” Wu explains.

“Interestingly, this idea of using higher-intensity cardio while trying to preserve muscle isn’t new,” Anna Di, D.C., C.E.S., a corrective exercise specialist, chiropractor, and owner of UNITY Chiropractic Wellness in New York City, points out. “It’s one of the reasons many competitive bodybuilders choose HIIT during fat loss phases because they’re trying to maintain as much lean muscle as possible while reducing body fat. They’re obviously training for a very different goal than the average person, but the concept is similar.”

What’s significant about this study, according to Di, is that it observes the same benefits in relatively healthy older adults, making the benefits of HIIT more widely applicable.

Does HIIT exercise have other benefits?

Burning fat and building muscle aren’t the only reasons to consider building HIIT into your regular workout routine. “HIIT has been shown in many studies to improve cardiovascular fitness, blood sugar regulation, and overall conditioning,” Di explains.

That doesn’t mean it’ll be a good fit for everyone. Higher-intensity exercise also comes with a greater risk of injury, which is why Di cautions anyone with underlying health conditions, balance issues, or who isn’t used to regular exercise against jumping in without consulting a doctor.

“Individuals with cardiovascular conditions that are not well controlled, poor core/pelvic weakness, or significant joint problems should avoid HIIT due to the high-impact forces,” Wu adds. “People with elevated stress and poor management should not participate as HIIT can spike cortisol levels.”

What does this mean for you?

As long as you’re in relatively good health and have cleared any concerns with a doctor, starting to incorporate HIIT into your routine can’t hurt, especially the older you get. “Maintaining muscle mass becomes increasingly important as we age because muscles are what give us strength, mobility, and balance,” Di explains. “Muscle also plays an important role in regulating blood sugar.”

Holding onto precious muscle mass can even affect your body in ways you probably haven’t considered. “Something many people don’t realize is that muscles are also what pull on our bones,” Di points out. “That mechanical stress is one of the signals that helps bones stay thicker and stronger over time, which is especially important as we get older and for women after menopause when the risk of osteoporosis increases.”

That doesn’t mean you should throw low- and moderate-intensity exercise out the window. “The biggest takeaway is that both high-intensity and moderate-intensity exercises worked. Both reduced body fat, which is really the goal for many people,” Di says. She also points out that the low-impact exercises the study participants performed (stretching and toning classes) have other benefits like improved flexibility, mobility, and balance that weren’t necessarily captured by the results.

“Yes, preserving muscle is important, but the amount of lean muscle loss in the moderate-intensity group was actually very small,” Di reiterates. “For someone who’s older, new to exercise, or simply doesn’t enjoy high-intensity workouts, a regular walking program may still be an excellent option if it’s something they’ll consistently do.”

The bottom line

The results are clear: HIIT exercise has a key advantage if your goal is to lose fat while holding onto muscle. But the most important thing is exercising regularly in the way that works best for you. All three exercise interventions the researchers used had their benefits, so it comes down to listening to your body and knowing what your goals are.

“In my opinion, consistency is much more important than chasing a small difference in muscle preservation if the alternative is not exercising at all,” Di explains, pointing out that the study primarily used heart rate to measure exercise intensity, which means that a power walk might feel just as intense to one person as a run might feel to someone else. Ultimately, “the best exercise is usually the one you’ll continue doing months and years from now.”