Aging is a natural process associated with a decline in cognition. However, the mediating effect of physical function and circulating myokines on this relationship has yet to be fully clarified. This study investigated how muscle strength and circulating insulin-like growth factor-1 (IGF-1) levels mediate the relationship between age and cognitive functions. A total of 1255 participants aged 25–74 years included in the Midlife in the United States II study were retrospectively analyzed. In this cross-sectional analysis, we applied a serial mediation model to explore the mediating effects of muscle strength and circulating IGF-1 levels on the relationship between age and cognitive functions. We included potential confounding factors related to sociodemographics, lifestyle, and health status as covariates in the model. The results showed that aging had both direct and indirect effects on cognition. As predicted, muscle strength and IGF-1 levels mediated the relationship between age and specific cognitive functions. In addition, mediation analyses indicated that the association between aging and cognitive flexibility, immediate and delayed memory, and inductive reasoning were partially mediated by muscle strength and IGF-1 levels in a serial manner. Our study demonstrated the serial multiple mediation roles of muscle strength and IGF-1 levels on the relationship between age and specific cognitive functions. Further longitudinal research should be performed to confirm the serial mediation results.

中文翻译：

---

下半身肌力和IGF-1水平在年龄与认知关系中的中介作用MIDUS 子研究

衰老是与认知能力下降相关的自然过程。然而，身体功能和循环肌因子在这种关系中的中介作用尚未完全阐明。这项研究调查了肌肉力量和循环胰岛素样生长因子 1 (IGF-1) 水平如何调节年龄和认知功能之间的关系。对美国中年 II 研究中纳入的 1255 名 25-74 岁参与者进行了回顾性分析。在这项横断面分析中，我们应用串行中介模型来探讨肌肉力量和循环 IGF-1 水平对年龄和认知功能之间关系的中介作用。我们将与社会人口统计、生活方式和健康状况相关的潜在混杂因素作为模型中的协变量纳入其中。结果表明，衰老对认知有直接和间接的影响。正如预测的那样，肌肉力量和 IGF-1 水平介导了年龄和特定认知功能之间的关系。此外，中介分析表明，衰老与认知灵活性、即时记忆和延迟记忆以及归纳推理之间的关联部分是由肌肉力量和 IGF-1 水平以连续方式介导的。我们的研究证明了肌肉力量和 IGF-1 水平对年龄和特定认知功能之间关系的连续多重调节作用。应进行进一步的纵向研究以确认系列中介结果。