Moderate workouts cost older adults some muscle while interval training did not, a six-month study found

Older adults who spent six months in a supervised treadmill program at a moderate pace lost some fat and also some lean tissue, while adults who did interval training for the same six months lost fat and kept their lean mass. The lean-tissue loss in the moderate group showed up within the first three months. That split comes from a trial of 123 healthy Brisbane-area adults with an average age of 72, led by exercise physiologist Grace Rose at the University of the Sunshine Coast.

The work was published in the journal Maturitas in 2025, and the university publicised it on January 23, 2026. The trial is a six-month comparison, and the lean-mass gap it reports is small.

The lean-mass result is the part that drew attention. Rose noted in the university release that body composition is implicated in the progression of many chronic diseases as people get older, and the trial was built to ask which kind of exercise shifts that composition in the right direction, fat down and lean tissue steady, in people already past 70.

Three Groups, Three Sessions a Week

The abstract on the James Cook University repository record describes a sub-study of a randomised controlled trial registered as ACTRN12618000700235. Every participant attended three supervised 45-minute sessions a week for six months, with heart-rate targets set for each person. Of the 123 adults, 45 were assigned to moderate-intensity treadmill training, 41 to high-intensity interval training, and 37 to a low-intensity active control group. The mean body mass index was 25.8.

Body composition was measured by dual-energy X-ray absorptiometry, the DXA scan, at the start, at three months and at six months. Interval training alternates repeated short bursts of very hard effort with easier recovery periods; in the university’s description, breathing is heavy and conversation is difficult during the hard bursts.

Lean Mass: Where the Groups Split

Fat loss was shared. Both the interval group (p = 0.001) and the moderate group (p = 0.016) reduced fat mass, and both reductions were larger than the control group’s. Lean tissue is where they diverged: only the moderate-intensity group lost fat-free mass, at the zero-to-three-month mark (p = 0.005) and across the full zero-to-six-month span (p = 0.050), the latter sitting right on the conventional significance line. At six months the interval group showed a higher raw lean-mass value than the moderate group (p = 0.042).

Rose said in the University of the Sunshine Coast release that high, medium and low intensity exercise all led to modest fat loss, but “only HIIT retained lean muscle.” She added that moderate training reduced fat mass but also caused a small decline in lean muscle. Associate Professor Mia Schaumberg, a co-author, offered a mechanism: interval work places more stress on the muscles, which she said signals the body to hold on to muscle tissue.

The low-intensity group, which served as the active control, is the least settled arm. The university release says its results need further analysis, so the comparison that matters most is the one between the two harder-working groups, moderate training against intervals, with the control group serving mainly as the yardstick for how much fat each of them shed.

DXA Lean Mass Versus Muscle Strength

A DXA scan reports lean mass, a category that includes water and other soft tissue besides muscle fibre, and the trial’s headline measure is therefore a body-composition number and not a strength test. A small slide in lean mass does not translate one-for-one into weaker legs, and the paper does not claim it does.

The authors’ own conclusion is restrained. They describe the changes as small and not clearly clinically meaningful when compared with lower-intensity exercise, particularly once measurement error in the scan is accounted for, and they suggest higher-intensity training may be considered where it is appropriate and feasible. The participants were healthy, so the findings do not speak to older adults with health conditions or mobility limits, a point Medical News Today also flagged in its account.

The Australian Science Media Centre carried the work on SCIMEX on January 21, 2026, naming the Stafford Fox Medical Research Foundation as funder and collaborators at the University of Queensland, University of Southern Queensland, UNSW and James Cook University. That page tags the work as observational, while the journal record describes a sub-study of a randomised controlled trial; the allocation to exercise type is the journal’s account and the one used here. A later October summary of the paper repeats the same split: moderate training lowered fat and nudged lean mass down, interval training lowered fat without the lean-mass loss. What the Maturitas record does not settle is whether the gap would widen, close or matter for falls and independence over years, because the trial stopped at six months.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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