HIIT: A METHOD FOR RETAINING MUSCLE AS YOU AGE

Source: University of the Sunshine Coast

Losing fat is good. Losing muscle along with it? Not so much—especially later in life, when muscle plays a major role in strength, balance, mobility, and independence.

A six-month study suggests high-intensity interval training, better known as HIIT, may help older adults avoid that trade-off. While both high- and moderate-intensity exercise reduced body fat, only HIIT preserved lean tissue.

“We found that high, medium and low intensity exercises all led to modest fat loss, but only HIIT retained lean muscle,” said lead author and exercise physiologist Dr. Grace Rose of the University of the Sunshine Coast.

The findings point to an important lesson: healthy aging isn’t simply about losing weight. What you lose matters.

Six Months of Exercise Revealed a Key Difference

The Australian research team studied 123 healthy older adults from the Greater Brisbane region. Participants were 72 years old on average and had an average body mass index of about 26 kg/m², which the researchers described as normal for adults over 65.

For six months, participants completed three supervised gym sessions each week. Every session lasted 45 minutes, and each person was assigned to one of three groups:

• High-intensity interval training
• Moderate-intensity exercise
• Low-intensity exercise

Researchers measured participants’ body composition before the program, after three months, and again at six months. Specialized scans estimated fat and lean tissue across the body.

All three groups experienced modest fat loss, but exercise intensity affected the results.

Both HIIT and moderate-intensity training reduced more fat than low-intensity exercise. The difference emerged when researchers examined lean tissue.

“While moderate training reduced fat mass, it also caused a small decline in lean muscle,” Rose said.

The HIIT group reduced fat without experiencing the same decline in lean mass.

That distinction becomes more important with age. Muscle helps people climb stairs, rise from a chair, carry groceries, maintain balance, and stay independent.

One caveat: the scans measured lean tissue, not muscle strength. Lean mass includes muscle, water, and other nonfat tissues, so preserving it does not necessarily mean participants became stronger.

HIIT Also Targeted Fat Around the Waist

The study found another possible benefit. Both high- and moderate-intensity exercise improved body composition around the middle, including reductions in visceral fat.

“Both high and moderate intensities improved the composition of weight carried around the middle,” Rose said. “Further analysis is needed of the low-intensity results.”

Visceral fat sits deep inside the abdomen and surrounds organs such as the liver and intestines. It differs from the softer fat stored directly beneath the skin.

Too much visceral fat has been linked to insulin resistance, cardiovascular disease, and other metabolic conditions. That makes its reduction potentially more important than a simple change on the scale.

Body weight and BMI can provide a rough picture of health, but they cannot show how much fat or muscle someone carries—or where the fat is stored. Two people can lose the same amount of weight and experience very different outcomes. One might lose mostly fat, while the other loses both fat and valuable lean tissue.

The researchers stressed that the improvements in this study were relatively small. Once measurement uncertainty was taken into account, the differences were not clearly large enough to be considered clinically meaningful compared with low-intensity exercise.

So HIIT showed promise, but it wasn’t a miracle fix.

Why HIIT May Protect Aging Muscles

HIIT alternates short bursts of hard work with easier recovery periods. Instead of maintaining the same pace from beginning to end, participants repeatedly pushed their cardiovascular systems and muscles, then briefly backed off.

Associate Professor of Physiology Mia Schaumberg, a study co-author, described the hard intervals as periods when breathing becomes heavy and conversation is difficult.

“HIIT likely works better because it puts more stress on the muscles, giving the body a stronger signal to keep muscle tissue rather than lose it,” she said.

That explanation fits a basic principle of exercise: the body adapts to what it is asked to do. When muscles face a demanding stimulus, the body has more reason to preserve the tissue needed to meet that demand.

This matters because muscle mass and strength naturally tend to decline with age. In more serious cases, that decline can contribute to sarcopenia, a condition that affects mobility, physical function, and independence.

The study brought together researchers from the University of the Sunshine Coast’s Healthy Aging Research Cluster and the University of Queensland.

Newer Research Adds Some Nuance

Other studies published in 2026 have found additional benefits from HIIT, though they also suggest it may not always outperform moderate exercise.

One study in Medicine & Science in Sports & Exercise examined whether older adults could complete HIIT at home with remote supervision. It involved 20 adults aged 61 to 74.

Participants trained on a specialized machine that allowed them to exercise their arms and legs without bearing their full body weight. After eight weeks, they had lost an average of roughly 1.4 kilograms—or about 3 pounds—of fat. Their aerobic fitness also improved considerably.

The participants completed 96 percent of their scheduled workouts, and researchers reported no exercise-related adverse events.

It was a small study, so its results should be treated cautiously. Still, it suggests that carefully designed and supervised HIIT programs may work outside a conventional gym.

A separate randomized trial published in The Journals of Gerontology, Series A compared HIIT with continuous moderate-intensity exercise among older adults living with HIV.

Participants exercised for 16 weeks, and both groups also performed resistance training. In this case, both groups lost fat and gained lean mass. Researchers found no statistically significant difference in body-composition changes between them.

That doesn’t necessarily conflict with the Australian findings. The studies involved different populations, training plans, and durations. The second trial also included resistance training, which is specifically designed to challenge muscles and can help preserve or build lean tissue.

The takeaway is pretty simple: intensity matters, but it isn’t the only thing that matters.

Is HIIT the Best Exercise for Older Adults?

A broader review published in the Journal of Clinical Medicine in August 2026 examined 25 reports involving about 2,818 participants.

The clearest and most consistent benefit of HIIT was improved cardiovascular fitness, including better oxygen use during exercise. Some studies also found gains in physical function and metabolic health.

The review did not establish that HIIT consistently beats moderate-intensity exercise.

The programs varied widely. So did the participants, workout schedules, and methods used to measure results. Those differences made it difficult to identify one ideal training approach for every older adult.

HIIT can be a useful part of healthy aging, but it isn’t the only option. For adults over 65, the Centers for Disease Control and Prevention recommends a mix of aerobic activity, muscle-strengthening exercise, and balance work.

Someone who has been inactive—or who lives with heart disease, joint problems, or another medical condition—shouldn’t jump straight into all-out intervals. Building up gradually and getting guidance from a qualified healthcare or exercise professional can make demanding workouts safer and more sustainable.

The most useful lesson from the Australian study has less to do with any single workout and more to do with how we define progress.

A lower number on the scale doesn’t tell the whole story. Losing fat while preserving the muscle needed to move, balance, and live independently may be the better goal. In this study, HIIT showed real promise in helping older adults do exactly that.