Leg Muscle Strength as a Protective Factor Against Cognitive Aging: Evidence from a 10-Year Twin Study

Cognitive decline is a major concern of aging populations, affecting memory, processing speed, and overall quality of life. While physical activity has long been associated with better brain health, the specific biological factors linking physical fitness to cognitive aging have remained unclear. A landmark longitudinal study titled “Kicking Back Cognitive Ageing: Leg Power Predicts Cognitive Ageing after Ten Years in Older Female Twins” provides compelling evidence that muscle strength itself—particularly leg power—plays a direct and protective role in maintaining cognitive function and brain structure over time.

This study followed 324 healthy female twins in the United Kingdom over a 10-year period, making it one of the most methodologically rigorous investigations into the relationship between physical strength and brain aging. Participants underwent objective leg power testing in midlife, along with repeated assessments of cognitive performance over the following decade. Cognitive outcomes included memory, processing speed, and global cognitive ability. In a subset of participants, brain magnetic resonance imaging (MRI) was also used to assess structural changes, including total gray matter volume.

The findings were striking. Women with greater leg muscle strength at baseline experienced significantly slower cognitive decline over the 10-year follow-up period. Higher leg power was consistently associated with better memory retention, faster thinking speed, and stronger overall cognitive performance. Importantly, these cognitive benefits were paralleled by structural brain differences. Participants with stronger leg muscles showed greater total gray matter volume on MRI scans, a key marker of brain health and resilience against neurodegeneration.

One of the most powerful aspects of this study was its use of identical twin pairs. By comparing twins who share the same genetic makeup and early-life environment, the researchers were able to control for two major confounding factors that often limit observational studies. Differences in cognitive aging between twins could therefore be attributed more confidently to differences in leg muscle strength rather than genetics, childhood conditions, or socioeconomic background. This design provides unusually strong evidence for a causal relationship between muscle strength and brain aging.

Crucially, the results suggest that muscle strength is not merely a proxy for general physical activity or overall health. Instead, leg power itself appears to exert a direct protective effect on the brain. Potential mechanisms include improved metabolic regulation, enhanced insulin sensitivity, reduced systemic inflammation, and increased production of neurotrophic factors that support neuronal survival and plasticity. Stronger muscles may also promote more efficient neural signaling between motor and cognitive networks, reinforcing brain resilience over time.

In conclusion, the Kicking Back Cognitive Ageing study demonstrates that maintaining leg muscle strength in midlife is a powerful predictor of healthier cognitive aging and preserved brain structure in later life. By leveraging a long-term twin design, the research provides robust evidence that muscle strength itself plays an active role in protecting the aging brain. These findings underscore the importance of strength-based interventions—not just aerobic exercise—as a key strategy for preserving cognitive function and brain health across the lifespan.

Reference:
Steves, C. J., Mehta, M. M., Jackson, S. H. D., & Spector, T. D. Kicking Back Cognitive Ageing: Leg Power Predicts Cognitive Ageing after Ten Years in Older Female Twins.