Age-related muscle loss, known as sarcopenia, is a major health burden for older adults. A new paper argues that doctors have explained only half of why people get weaker, and that the missing half may lie in the nervous system.
A common problem with serious consequences
Sarcopenia affects up to 29% of community-dwelling older adults, and rates are higher in hospitals, residential care and among frail patients. It contributes to disability and loss of independence, and falls are its clearest consequence. In Australia, there were 253,800 fall-related hospitalizations in 2024–25. In the year before, 6,722 people died following a fall, and fall injuries cost the health system an estimated $5.4 billion. As MedicalXpress reports, Australian primary care is now being asked to screen for poor muscle health.
The definition moved, the explanation didn’t
Diagnosis has already shifted away from muscle mass. Grip strength, gait speed and chair stands now define sarcopenia because they predict falls, disability and death better. Yet the explanation still treats weakness as a simple result of shrinking muscle.
Lucas Orssatto of the University of Queensland and colleagues argue in The Lancet Healthy Longevity that the evidence doesn’t support this. Muscle loss explains only a modest share of age-related strength decline, and two people with the same muscle mass can differ greatly in strength and mobility. Drugs and protein strategies reliably build muscle but deliver disappointing gains in what people can actually do. Exercise, meanwhile, improves strength and mobility even when muscle mass doesn’t measurably change.
A whole-system problem
Their proposal is that ageing degrades the entire motor system: the brain, spinal cord, nerves and their connections to muscle. Movements are planned more slowly, signals travel less reliably and arrive weaker, and balance and position sense fade. The muscle may still be there, but less of the command reaches it.
Standing up from a chair shows why this matters. It is a task of speed and power, not bulk. Power declines earlier and faster than muscle mass, and it depends heavily on how well nerves recruit and drive muscle fibers.
What clinicians could watch for
The authors suggest sarcopenia is better understood as a disease of the aging motor system, and they set out a five-point agenda for the groups that write diagnostic criteria. For primary care physicians, strength and gait speed stay. Alongside them, they suggest noting:
- how quickly a patient rises from a chair, not just whether they can
- unsteadiness during sustained effort
- hand dexterity
- how walking changes when a conversation is added
Weakness that is asymmetric, rapid or out of proportion to muscle loss deserves a closer look. Sedative and anticholinergic medications blunt motor drive, so medication review belongs alongside strength training.
The honest limits
The authors acknowledge that nobody has yet shown these measures beat existing screens, on outcomes or cost, and neuromuscular expertise isn’t evenly available in primary care. They call for validated practical tests, staged guidelines and trials that measure nerve as well as muscle.
The potential payoff is better identification of why an individual is weakening, more targeted treatment, and a shift in research and health care investment away from muscle-mass-focused approaches toward multicomponent interventions that improve strength, movement and everyday function.
Source: Weakness and mobility loss in aging are not just muscle problems, MedicalXpress, by Lucas Orssatto, University of Queensland.
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