Muscles still grow after 65, but lean mass scans may not show it

Muscle shrinks with age, and that loss sits behind frailty, falls and lost independence. Resistance training is the standard countermeasure, but two questions hang over it in older populations: whether muscle past 65 retains a genuine capacity to grow, and whether the tools used to measure that growth agree with each other. Trials in older adults have variously used scans of whole-muscle size, biopsies of individual fibres and estimates of leg lean mass, and if those measures tell different stories, both researchers and lifters risk drawing the wrong conclusions about whether a programme is working.

The authors systematically searched PubMed, Embase and Scopus for randomised controlled trials of supervised resistance training in adults aged 65 and older. Eligible trials reported muscle size, muscle fibre area or leg lean mass as outcomes. Thirty-two studies made it into the review and 28 were pooled statistically. The team then ran a meta-regression to test whether age, weekly training volume or programme duration explained differences between trials in how much muscle and fibre growth occurred.

Resistance training had a significant effect on whole-muscle size and a somewhat larger one on muscle fibre area. Leg lean mass, by contrast, did not change significantly. A subanalysis restricted to studies measuring quadriceps size also found a significant effect. In the regression, programme duration significantly influenced type II fibre area, while neither weekly sets nor age showed a significant influence on any outcome. The authors conclude that lean mass measures may simply not capture the adaptations resistance training produces.

This strengthens an already substantial body of work showing that ageing muscle remains trainable, and it adds a useful methodological twist: leg lean mass, one of the most common outcomes in ageing research, may fail to register growth that imaging and fibre-level measurement detect. The absence of an age effect within this older group is quietly reassuring, suggesting the response does not collapse with advancing years. Why duration mattered for type II fibres, and which programme features best drive growth in this population, remain open questions.

For anyone lifting in later life, or encouraging a parent to start, this is a reason for confidence that the muscle itself responds, at both the whole-muscle and the fibre level. It is equally a reason to be sceptical of a flat lean mass reading on a body composition scan, since that measure sat still here while muscles measurably grew. Strength and directly measured muscle size told the more accurate story in these trials.