Researchers at the University of the Sunshine Coast followed 123 healthy older adults, average age 72, for six months. Participants completed three supervised gym sessions per week, assigned to either high-intensity interval training, moderate-intensity exercise, or a low-intensity comparison group. Body composition was measured at the start, after three months, and at the end of the trial using a specialized scanning technique. Results published in Maturitas showed that high- and moderate-intensity training both led to significant fat loss, but they differed in their effect on lean tissue.
Moderate-intensity exercise reduced fat mass but also caused a small decline in lean muscle. HIIT, by contrast, reduced fat without the same loss of lean mass. Both high- and moderate-intensity training also improved visceral fat, the deeper abdominal fat linked to metabolic risk. Lead author Dr. Grace Rose said that while all intensities produced modest fat loss, only HIIT retained lean muscle.
The distinction matters for healthy aging because maintaining muscle supports strength and independence. However, the authors emphasized that the improvements were relatively small and not clearly clinically meaningful compared with lower-intensity exercise once measurement uncertainty was considered. They also noted that the scans measured lean tissue, not muscle strength directly, so the findings do not necessarily translate into equivalent strength gains.