THE ARISING · Longevity & Healthspan
Interval Training Kept Lean Mass in Older Adults, but Changes Were Small
Losing fat is easy to celebrate. Losing fat without losing lean tissue is the harder goal in later life. A six-month randomised trial suggests exercise intensity may play a part, though the gains were small. The trial measured lean mass, which includes muscle but also other tissues, not muscle itself.
The study, published in the journal Maturitas in 2025, was a randomised controlled trial, the strongest design for testing whether an intervention causes a change. It was a sub-study of a larger trial and included 123 healthy older adults with an average age of 72 years and an average body mass index of 25.8.
All participants did three supervised 45-minute exercise sessions a week for six months. They were randomly assigned to one of three groups: treadmill-based moderate-intensity training (45 people), high-intensity interval training, or HIIT (41 people), or a low-intensity active control condition (37 people). Heart-rate targets were set for each individual. Body composition was measured with dual-energy xray absorptiometry, a scan that estimates fat and lean tissue, at the start, at three months and at six months.
Both the HIIT and moderate-intensity groups lost fat mass, and by similar amounts. Both reductions were larger than in the low-intensity control group, according to the authors.
The groups differed on lean tissue. Only the moderate-intensity group showed reductions in fat-free mass, which includes muscle and other lean tissues. The authors noted this could potentially add to the age-related loss of muscle and other lean tissue. At six months, the HIIT group had a greater raw difference in lean mass than the moderate group. HIIT was also the only group with a net improvement in body fat percentage.
Both HIIT and moderate-intensity training also improved visceral adipose tissue over six months. This is fat stored deep in the abdomen, around internal organs. The improvements were comparable between the two groups.
The authors were careful about how much to read into this. Their conclusion was that HIIT reduced fat and maintained lean mass, but that the changes were small. They said the changes were not clinically meaningful compared with exercise of lower intensity, once measurement error was considered. This is where the argument is weakest: the lean-mass difference is small, and whether it matters for strength or daily life is not shown.
A press report from ScienceDaily, covering a University of the Sunshine Coast release, quoted lead author Dr. Grace Rose as saying: "We found that high, medium and low intensity exercises all led to modest fat loss but only HIIT retained lean muscle." ScienceDaily also quoted co-author Associate Professor Mia Schaumberg, who said HIIT likely works better because it puts more stress on the muscles, giving the body a stronger signal to keep muscle tissue. That is her explanation.
For healthy older adults, the practical message is cautious. In this trial, HIIT was compared with moderate training as separate programmes; it did not test adding intervals to steady cardio, so that idea is our suggestion, not a finding. The trial does not show a large benefit. The authors say higher-intensity training may be considered "where appropriate and feasible." In the coverage, HIIT meant short bursts of very hard effort, with heavy breathing and difficult conversation, alternated with easier recovery periods. That is demanding. The participants here were healthy, so the results may not apply to people with chronic illness.
A separate 2026 study in Medicine and Science in Sports and Exercise tested homebased HIIT with remote supervision in 20 older adults aged 61 to 74. It reported no adverse events related to the training and 96% completion of sessions. It had no comparison group of different intensities, so it speaks to feasibility rather than to which intensity is best. What to watch next: trials that measure strength and everyday function alongside body composition, to show whether the small differences in lean mass matter in daily life.
BlackRock Buys Majority Stake in Humana's CenterWell Senior Clinics for $2.8 Billion South Korea Labor Minister Says Retirement Age Law Must Pass This Year UBS UK Pension Plan Completes £1.7 Billion Buy-In With L&G Congress Passes Bill Renaming Social Security Claiming Ages to Encourage Later Claiming CareTrust REIT Buys £1.1 Billion UK Care Home Portfolio From LNT