Supplementary Material for: Kicking Back Cognitive Ageing: Leg Power Predicts Cognitive Ageing after Ten Years in Older Female Twins

<b><i>Background:</i></b> 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. <b><i>Objectives:</i></b> 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. <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> 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. <b><i>Conclusion:</i></b> 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.

**背景：** 既往多项观察性研究均证实，体力活动对认知衰老具有保护作用，但相关干预性研究的结论说服力欠佳。这一现象可能源于干预周期过短、干预方案未达最优，或干预缺乏持久效应；此外，常见遗传与发育因素带来的混杂偏倚也难以排除。
**目的：** 本研究旨在验证，在健康老年人群中，肌肉健康水平（以腿部力量为衡量指标）是否可预测10年随访期内的认知变化；同时评估该指标与其他认知衰老预测因子的联合预测效能，并探究该效应是否受双生子共享因素的混杂影响。此外，本研究还针对同卵双生子对（monozygotic pairs），探讨12年随访期间腿部力量差异是否可预测脑结构与功能的变化。
**方法：** 本研究共纳入324名健康女性双生子，基线平均年龄为55岁（范围43~73岁），所有受试者在间隔10年的两个时间点均接受了剑桥神经心理测试自动化成套测验（Cambridge Neuropsychological Test Automated Battery, CANTAB）。采用线性回归模型分析基线腿部力量、体力活动与后续认知变化之间的关联，并全面校正基线混杂变量，包括心脏病、糖尿病、血压、空腹血糖、血脂、饮食状况、体格特征、烟酒习惯、阅读智商、社会经济地位及出生体重。采用双生子不一致配对分析法校正双生子共享因素。随后选取部分同卵双生子对进行磁共振成像（magnetic resonance imaging, MRI）检查，通过线性回归模型及配对t检验分析肌肉健康水平与脑结构、功能之间的关联。
**结果：** 研究发现肌肉健康水平（腿部力量）与10年认知变化[完全校正模型的标准化β系数（Stdβ）=0.174，p=0.002]及后续总灰质体积（Stdβ=0.362，p=0.005）之间均存在显著的保护关联。在双生子不一致配对分析中，该效应依然稳健：双生子对间的体能差异同样可预测侧脑室体积的组内差异。自我报告的体力活动仅存在微弱的独立预测效应。
**结论：** 即便校正了双生子共享的常见遗传因素与早期生活环境，腿部力量仍可预测认知衰老及全脑结构变化。长期针对性提升腿部力量的干预措施，或有助于实现健康认知衰老的通用目标。