High-intensity interval training helped healthy older adults reduce body fat while preserving their lean mass, according to an Australian study published in Maturitas. Moderate-intensity exercise also reduced fat, but was accompanied by a small decline in lean mass. The finding highlights the importance of body composition during ageing: weight loss alone does not show which tissues are being lost. However, the researchers stress that the improvements were relatively small and did not establish a clear, clinically meaningful advantage over lower-intensity exercise.
The University of the Sunshine Coast team followed 123 healthy older adults from the greater Brisbane area, with an average age of 72. Their average body mass index was about 26 kilograms per square metre, a value the researchers described as normal for people over 65. Participants were assigned to three groups: high-intensity interval training, moderate-intensity exercise and low-intensity exercise as a comparison group. For six months, they attended three supervised gym sessions a week, each lasting 45 minutes.
Body composition was measured at the start, after three months and at the end of the six-month period, using a specialised scanning method that estimates fat and lean mass. Lead author and exercise physiologist Grace Rose said all three intensities were associated with a small loss of fat. The reduction was statistically significant in the high- and moderate-intensity groups, with greater improvements than in the low-intensity group. The difference between the two more demanding programmes concerned lean mass, which was preserved in the interval training group.
The distinction between lean mass and muscle strength is crucial to interpreting the results. The scans did not measure strength directly, and lean mass includes other tissues and water as well as muscle. Preserving it therefore does not prove a corresponding preservation or increase in strength. Even so, protecting muscle is particularly important in older age, as it supports everyday activities such as climbing stairs, getting up from a chair and maintaining balance.
The high- and moderate-intensity groups also showed improvements in visceral fat, while, according to Rose, the low-intensity results need further analysis. Visceral fat accumulates deeper in the abdomen, around organs such as the liver and intestines, and differs from the fat beneath the skin. Excessive accumulation has been linked to insulin resistance, cardiovascular disease and other metabolic disorders. Weight and body mass index do not capture this distribution, but the researchers warned that uncertainty in the measurements limits conclusions about the clinical significance of the differences.
High-intensity interval training, known as HIIT, alternates short bursts of very demanding effort with easier recovery periods. Co-author and associate professor of physiology Mia Schaumberg explained that, in this study, the intense intervals caused heavy breathing and made conversation difficult. In her view, the greater strain on the muscles may give the body a stronger stimulus to preserve muscle tissue. This is a possible explanation for the finding, which is of interest because ageing is often accompanied by a gradual loss of muscle mass and strength.
A small 2026 study examined whether HIIT could be done at home with remote supervision. It involved 20 adults aged 61 to 74, who used a specialised machine to exercise their arms and legs without having to support their body weight. After eight weeks, they had lost an average of about 1.4 kilograms of fat and significantly improved their aerobic fitness. They completed 96% of the scheduled sessions, and no exercise-related adverse events were reported, although the small sample limits how widely the findings can be applied.
Another randomised study in 2026, involving older adults living with HIV, compared HIIT with continuous moderate-intensity exercise over 16 weeks. Both groups also did resistance training and showed a reduction in fat and an increase in lean mass, with no statistically significant difference between them. The result suggests that intensity is not the only factor that matters and that resistance training may also help preserve or increase lean mass. Because the populations and programmes differed, the findings do not directly contradict the Australian study.
A broader review in the Journal of Clinical Medicine examined 25 publications involving about 2,818 participants and found the most consistent benefits of interval training in cardiorespiratory fitness. However, it did not find a consistent advantage for HIIT over moderate-intensity exercise, as differences between programmes and participants made it difficult to identify an optimal approach. For people over 65, the Centers for Disease Control and Prevention recommend a combination of aerobic exercise, muscle strengthening and balance exercises. High intensity may suit some people, while those who are inactive or have health problems may benefit from gradually building their fitness and seeking guidance before starting a demanding programme.
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