A six-month study suggests a way to help older adults lose fat while keeping the muscle that keeps them strong. Researchers from the University of the Sunshine Coast compared three exercise intensities in 123 healthy older adults and found that all three produced modest fat loss, but only high-intensity interval training (HIIT) did so without the small decline in lean muscle that came with moderate-intensity exercise. HIIT alternates short bursts of hard effort with easier recovery periods. The trial was published in the journal Maturitas.
The researchers noted that the improvements were small and that the differences were not clearly clinically meaningful compared with lower-intensity exercise once measurement uncertainty was taken into account.
What did the study find?
Both high- and moderate-intensity training reduced fat mass more than the low-intensity group did. The two approaches parted ways on lean tissue: moderate training came with a small loss of lean muscle, while the HIIT group reduced fat without that decline. Lead author and exercise physiologist Dr. Grace Rose summarized the result this way: "We found that high, medium and low intensity exercises all led to modest fat loss but only HIIT retained lean muscle."
According to Rose, the distinction matters because body composition, meaning the proportions of fat, muscle and other tissues, can influence how chronic diseases develop as people age. Body weight and body mass index give general information but do not reveal how much fat or muscle a person carries or where fat is stored. Someone who loses fat while holding on to muscle may see a more favorable change than someone who drops a similar amount of weight along with lean tissue.
How was the study run?
The 123 participants were healthy older adults with an average age of 72 and an average body mass index of about 26 kg/m², which the researchers described as normal for adults over 65. Everyone completed three supervised gym sessions a week for six months, 45 minutes each, assigned to high-intensity intervals, moderate-intensity exercise or a low-intensity comparison group. Researchers measured body composition at the start, after three months and again at six months, using a specialized scanning technique that estimates fat and lean tissue throughout the body. The work involved collaborators from the university’s Healthy Ageing Research Cluster and The University of Queensland.
What happened to belly fat?
Both the high- and moderate-intensity groups improved the makeup of weight carried around the middle, with the study reporting reductions in visceral adipose tissue; the researchers said the low-intensity results need further analysis. Visceral fat sits deeper in the abdomen than the fat directly under the skin, surrounding organs such as the liver and intestines. Excess visceral fat has been linked to insulin resistance, cardiovascular disease and other metabolic problems.
Does keeping lean tissue mean stronger muscles?
The scans measured lean tissue, not muscle strength directly, so keeping lean mass does not automatically mean strength improved. Lean mass includes muscle along with other tissues and water. Holding on to muscle during fat loss still matters for staying independent: strong muscles help people climb stairs, get out of chairs, keep their balance and handle everyday tasks. Aging tends to bring a gradual loss of muscle mass and strength, which in more advanced cases can contribute to sarcopenia, a condition of reduced muscle strength and quantity that can interfere with mobility.
Why might HIIT protect muscle?
Associate Professor of Physiology and study co-author Mia Schaumberg described the high-intensity work as repeated short bursts of very hard exercise, "where breathing is heavy and conversation is difficult," alternated with easier recovery. She offered a possible reason for the result: "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." This was her proposed explanation, not a cause the study established.
Other work has looked at HIIT and lean tissue. A 2023 study in Frontiers in Physiology examined how HIIT affects lean mass, strength and power of the lower limbs in healthy older and younger people. A Harvard Health guide to HIIT for older adults notes that, according to studies, HIIT can increase fat-free mass, which includes muscle, by 1% to 3%, and that it helps maintain fast-twitch muscle fibers that naturally decline with age.
What do other 2026 studies show?
A 2026 study in Medicine & Science in Sports & Exercise tested whether older adults could do HIIT at home with remote supervision. Twenty adults aged 61 to 74 used a specialized machine that let them work their arms and legs without bearing their body weight. After eight weeks, participants lost an average of about 1.4 kilograms, roughly 3 pounds, of fat mass, their aerobic fitness improved substantially, they completed 96 percent of scheduled workouts, and the researchers reported no exercise-related adverse events. The trial was small, but its results suggest supervised HIIT may work outside a conventional gym.
A 2026 randomized trial in The Journals of Gerontology, Series A compared HIIT with continuous moderate-intensity exercise in older adults living with HIV. Over 16 weeks, both groups also did resistance training, both lost fat and gained lean mass, and there was no statistically significant difference between them in body composition. The populations and programs differed, so this does not directly contradict the Australian study; it points to resistance training as another way to preserve or build lean tissue.
Is HIIT the best exercise for older adults?
A systematic review published in the Journal of Clinical Medicine in August 2026 examined 25 reports involving about 2,818 participants. The most consistent benefit was cardiovascular fitness, including the body’s ability to use oxygen during exercise, and some studies also reported better physical function and metabolic health. The review did not establish that HIIT was consistently better than moderate-intensity exercise; its authors noted that differences in exercise programs, participant characteristics and study methods made it hard to identify one optimal approach. Harvard’s Nutrition Source makes a similar point, describing HIIT as useful for decreasing body fat and increasing strength and endurance but "not necessarily better than other exercise formats."
For adults over 65, the Centers for Disease Control and Prevention recommends a combination of aerobic exercise, muscle-strengthening activities and exercises that improve balance.
What to do now
- Work hard enough that talking gets difficult. In the study, the HIIT intervals were described as effort "where breathing is heavy and conversation is difficult." Harvard Health describes a talk test: if you cannot say more than a few words without taking a breath, you are at high intensity.
- Match the format behind the result. The findings came from three supervised 45-minute sessions a week over six months, not a one-time or unsupervised routine.
- Add strength and balance work alongside intervals.
- Build up gradually if you are inactive or have a medical condition. Harvard’s Nutrition Source advises that people who are deconditioned, elderly or have medical conditions be monitored closely by their physician and an exercise professional because of the higher intensity HIIT reaches.
- Track fat and lean tissue, not just the scale. Body-composition measurements show changes in fat and lean tissue that weight and body mass index miss.
FAQ
Did HIIT help older adults lose fat without losing muscle?
In the six-month University of the Sunshine Coast study of 123 healthy older adults, all three intensities produced modest fat loss, but only the HIIT group reduced fat without the small decline in lean muscle seen with moderate-intensity exercise. The researchers cautioned that the differences were relatively small.
How often did participants exercise in the study?
Participants completed three supervised gym sessions each week for six months, 45 minutes per session, assigned to high-intensity intervals, moderate-intensity exercise or a low-intensity comparison group.
Is HIIT better than other exercise for older adults?
The August 2026 Journal of Clinical Medicine review of 25 reports and about 2,818 participants did not establish HIIT as consistently better than moderate-intensity exercise; its most consistent benefit was cardiovascular fitness. The CDC recommends aerobic, muscle-strengthening and balance activities for adults over 65.
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