Tejal Somvanshi
Stronger legs were linked to healthier brain ageing in a 10-year study of 324 female twins — but what the research actually shows (and doesn’t show) might surprise you.
Researchers from King’s College London tracked 324 healthy female twins over a decade. They measured leg power — not muscle size, but the force and speed a person can generate when pushing against resistance. After 10 years, higher baseline leg power was associated with better cognitive performance and healthier brain structure compared to cognitive outcomes in their study co-twins who had lower baseline leg power.
The finding is genuine. It was peer-reviewed and published in the Gerontology journal. But it doesn’t answer the question many people ask: “If I strengthen my legs now, will my brain stay sharper?”
Why twins were studied
The researchers deliberately chose to study twin pairs. The sample included both identical and fraternal twins. This design helped researchers account for factors shared within pairs, including genetic influences and shared early-life environment. When twin pairs show different cognitive outcomes later in life despite shared genetics and early years — the difference is likely related to lifestyle or physical activity differences rather than genetics alone. It’s a powerful way to examine associations while accounting for inherited factors.
What “leg power” actually means
Leg power isn’t just muscle size. It’s measured using a pedal-rig apparatus that records how hard and how fast someone can push. A person might have large muscles but low power output, or average-sized muscles with excellent output. The study focused on output — the actual force and speed combination.
Researchers measured leg power at baseline. Participants completed cognitive tests assessing memory, processing speed and executive function at baseline and again 10 years later. A subset of monozygotic (identical) twin pairs underwent MRI brain scans to examine brain structure.
What they found
Twins with higher baseline leg power consistently scored higher on cognitive tests 10 years later. Higher baseline leg power was also associated with greater total grey-matter volume in the MRI subset. The difference held even after researchers adjusted for exercise, diet, sleep, smoking, education and other factors that affect brain health.
Why the association exists
Several mechanisms are plausible. Muscle contractions during exercise trigger the release of brain-derived neurotrophic factor (BDNF), a protein supporting brain cell survival and connection. Regular physical activity improves blood flow to the brain. And exercise-induced deep sleep may support brain metabolic clearance. But the study didn’t prove any of these mechanisms.
What the study doesn’t prove
The research is observational. It shows association, not causation. The study doesn’t prove that if you start a leg-strengthening programme now, your brain will definitely age more slowly.
The findings add to evidence that physical fitness and cognitive ageing are connected. Exercise benefits the brain through multiple mechanisms. The leg-power study provides one additional data point supporting physical activity as beneficial for healthy brain ageing.
