Most people past 70 are told to keep moving, but to take it easy. A brisk walk, a gentle swim, maybe a slow bike ride. For years that has looked like the safe choice.
A six-month trial of 123 healthy adults with an average age of 72 has pushed back on that picture. In the research, published in Maturitas, moderate exercise did trim fat, but it also quietly ate into lean muscle.
Only the group doing high-intensity interval training, or HIIT, kept their muscle while losing fat.
That matters because muscle loss with age makes falls more likely, saps strength and chips away at independence. Any workout that burns fat but also strips lean tissue leaves older adults further from those goals, not closer.
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What the researchers measured
The participants were based in Greater Brisbane and had an average body mass index of 26, which the researchers describe as normal for people over 65. Everyone trained three times a week for six months, with sessions lasting about 45 minutes.
They were split into three groups. One did high-intensity work, one did moderate work and one did low-intensity exercise. The researchers scanned their body composition at the start, at three months and at six months.
All three groups managed modest fat loss. But the lean muscle picture split them apart. HIIT held it steady. Moderate training saw a small decline. The low-intensity effect was less clear.
"We found that high, medium and low intensity exercises all led to modest fat loss but only HIIT retained lean muscle," said lead author Dr. Grace Rose. She is an exercise physiologist at the University of the Sunshine Coast.
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Why intensity may matter more than time
Her co-author, Associate Professor Mia Schaumberg, offered a mechanism. HIIT likely works better, she said, because it puts more stress on the muscles and gives the body a stronger signal to keep muscle tissue rather than lose it.
Both HIIT and moderate exercise also improved the composition of fat around the middle, the deep belly fat tied to heart and metabolic disease. On that measure, intensity did not seem to matter.
The research team also flagged a caveat. The improvements across all groups were modest, and once measurement uncertainty is factored in, the differences were not clearly clinically meaningful.
What HIIT means for someone in their 70s
HIIT does not have to mean sprinting. In the trial, it was short bursts of hard effort, where breathing was heavy and conversation was difficult, followed by easier recovery periods.
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On a stationary bike, that can be 30 seconds of pushing hard followed by a minute of easy pedaling, repeated.
Before trying it, Harvard Health advises older adults to consult a doctor, and to be extra cautious with heart disease, diabetes or high blood pressure. The guidance is to keep HIIT to two or three sessions a week, with rest days in between.
The trial's own protocol was three supervised 45-minute sessions a week for six months.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.