Summary
This study examined whether muscle fitness, specifically leg power, predicts cognitive ageing and brain structure over time. Researchers followed 324 healthy female twins (average age 55) for 10 years, assessing cognitive performance and controlling for numerous health and lifestyle factors. A subset of identical twins also underwent brain MRI scans after 12 years.
The results showed that higher leg power at baseline strongly predicted better cognitive performance over time and was associated with greater total grey matter volume. These findings remained significant even when comparing identical twin pairs, suggesting the relationship was not explained by shared genetics or early-life environment. Self-reported physical activity had only a weak independent effect.
Overall, the study suggests that muscle fitness, particularly leg strength and power, may play an important role in protecting brain health and slowing cognitive decline with age, highlighting the potential importance of long-term interventions that improve muscle strength for healthy cognitive ageing.
PMID: 26551663
PMCID: PMC4789972
DOI: 10.1159/000441029
Abstract
Background: Many observational studies have shown a protective effect of physical activity on cognitive ageing, but interventional studies have been less convincing. This may be due to short time scales of interventions, suboptimal interventional regimes or lack of lasting effect. Confounding through common genetic and developmental causes is also possible.
Objectives: We aimed to test whether muscle fitness (measured by leg power) could predict cognitive change in a healthy older population over a 10-year time interval, how this performed alongside other predictors of cognitive ageing, and whether this effect was confounded by factors shared by twins. In addition, we investigated whether differences in leg power were predictive of differences in brain structure and function after 12 years of follow-up in identical twin pairs.
Methods: A total of 324 healthy female twins (average age at baseline 55, range 43-73) performed the Cambridge Neuropsychological Test Automated Battery (CANTAB) at two time points 10 years apart. Linear regression modelling was used to assess the relationships between baseline leg power, physical activity and subsequent cognitive change, adjusting comprehensively for baseline covariates (including heart disease, diabetes, blood pressure, fasting blood glucose, lipids, diet, body habitus, smoking and alcohol habits, reading IQ, socioeconomic status and birthweight). A discordant twin approach was used to adjust for factors shared by twins. A subset of monozygotic pairs then underwent magnetic resonance imaging. The relationship between muscle fitness and brain structure and function was assessed using linear regression modelling and paired t tests.
Results: A striking protective relationship was found between muscle fitness (leg power) and both 10-year cognitive change [fully adjusted model standardised β-coefficient (Stdβ) = 0.174, p = 0.002] and subsequent total grey matter (Stdβ = 0.362, p = 0.005). These effects were robust in discordant twin analyses, where within-pair difference in physical fitness was also predictive of within-pair difference in lateral ventricle size. There was a weak independent effect of self-reported physical activity.
Conclusion: Leg power predicts both cognitive ageing and global brain structure, despite controlling for common genetics and early life environment shared by twins. Interventions targeted to improve leg power in the long term may help reach a universal goal of healthy cognitive ageing.