A six-month trial comparing three exercise intensities found that HIIT body composition outcomes in older adults differed from those produced by moderate or low-intensity training in one particular respect: high-intensity interval training preserved lean tissue while reducing fat mass, whereas moderate-intensity exercise reduced fat but also caused a small decline in lean muscle. The researchers caution, however, that the differences were not clearly clinically meaningful.
What the trial measured and who took part
The study, published in Maturitas, was conducted by researchers from the University of the Sunshine Coast. According to the university’s own account of the research, more than 120 healthy older adults from the Greater Brisbane region took part, completing three supervised gym sessions a week across six months. The report puts the total at 123 participants, with an average age of 72 and an average body mass index of approximately 26 kg/m², which the researchers described as normal for adults over 65.
Each session lasted 45 minutes. Participants were assigned to one of three groups: high-intensity intervals, moderate-intensity exercise, or a low-intensity comparison. Body composition was measured at the start of the trial, at three months, and again at six months, using a specialised scanning technique that estimates fat and lean tissue across the body.
‘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.
Both the high- and moderate-intensity groups showed greater reductions in fat mass than the low-intensity group. The meaningful distinction was in lean tissue: the moderate group experienced a small decline in lean muscle alongside the fat loss, while the HIIT group did not. The improvements were described by the researchers as relatively small, and they cautioned that the differences were not clearly clinically meaningful when compared with lower-intensity exercise, particularly after accounting for measurement uncertainty.
One further caveat: the scans measured lean tissue, not muscle strength directly. Lean mass includes muscle but also other tissues and water, so changes in these measurements do not automatically translate into equivalent changes in physical strength.
HIIT body composition benefits extended to abdominal fat
Beyond the lean tissue question, the study found that both high- and moderate-intensity training improved the distribution of fat around the middle of the body, including visceral adipose tissue. Visceral fat accumulates deeper in the abdomen, around internal organs, and has been linked to insulin resistance and cardiovascular disease. The researchers indicated that further analysis of the low-intensity group’s results in this area was needed.
Associate Professor of Physiology and study co-author Mia Schaumberg offered an explanation for why intensity might matter for muscle preservation. ‘High-intensity training in this study involved repeated short bursts, or intervals, of very hard exercise, where breathing is heavy and conversation is difficult, alternated with easier recovery periods,’ she said. ‘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.’
The background matters here. Ageing is often accompanied by a gradual loss of muscle mass and strength, which in more advanced cases can contribute to sarcopenia, a condition that can interfere with mobility and independence. The ability to lose fat without also losing lean tissue is therefore a different outcome from simply losing weight, and may be more useful for physical function over time.
How other 2026 research complicates the picture
The Australian findings sit alongside a growing body of work on HIIT in older populations, and not all of it points in the same direction. A 2026 randomised trial published in The Journals of Gerontology, Series A compared HIIT with continuous moderate-intensity exercise in older adults living with HIV, with both groups also performing resistance training. In that trial, both groups experienced reductions in fat and increases in lean mass, with no statistically significant difference between them. The researchers and the populations differed from the Australian study, so the results are not a direct contradiction, but they do suggest that resistance training may itself play a role in preserving lean tissue.
A separate 2026 home-based trial, published in Medicine & Science in Sports & Exercise, involved 20 adults aged 61 to 74 completing eight weeks of remotely supervised HIIT. Participants lost an average of approximately 1.4 kilograms of fat mass, their aerobic fitness improved, and they completed 96 per cent of their scheduled sessions with no reported adverse events. The trial was small, but its findings suggest that supervised HIIT outside a conventional gym setting may be feasible.
A broader review published in the Journal of Clinical Medicine, examining 25 reports and approximately 2,818 participants, found that HIIT produced consistent improvements in cardiovascular fitness in older adults but did not establish that it was consistently superior to moderate-intensity exercise across all outcomes. Differences in programme design, participant characteristics and study methods made a single optimal approach difficult to identify.
The Centers for Disease Control and Prevention recommends that adults over 65 combine aerobic exercise, muscle-strengthening activities, and balance work; intensity is one variable among several. The Australian study, published in Maturitas, adds to that picture by suggesting that what happens to lean tissue during fat loss may matter as much as the amount of weight lost, though the clinical magnitude of the difference remains an open question the researchers themselves raised.
