Supplementary Material for: Appendicular Muscle Mass, Thigh Intermuscular Fat Infiltration, and Risk of Fall in Postmenopausal Osteoporotic Elder Women

<b><i>Background:</i></b> The association between the quantity and composition of skeletal muscle and the decline in physical function in elderly is poorly understood. Therefore, the primary aim of this cross-over study was to investigate the association between thigh intermuscular adipose tissue (IMAT) infiltration, appendicular muscle mass, and risk of fall in postmenopausal osteoporotic elder women. Second, we examined the differences in muscle mass, IMAT, and risk of fall in the same sample of older subjects after being classified as sarcopenic or nonsarcopenic on the basis of the dual-energy X-ray absorptiometry (DXA)-based Appendicular Skeletal Muscle Mass Index (ASMMI). <b><i>Methods:</i></b> Twenty-nine subjects (age: 72.4 ± 6.8; BMI: 23.0 ± 3.3; and T-score: −2.7 ± 0.2) completed the following clinical evaluations: (1) whole-body DXA to assess the ASMMI; (2) magnetic resonance to determine the cross-sectional muscle area (CSA) and IMAT of thigh muscles, expressed both in absolute (IMAT_abs) and relative (IMAT_rel) values; and (3) risk of fall assessment through the OAK system (Khymeia, Noventa Padovana, Italy). The existence of a correlation between the risk of fall (OAK scores, an automated version of the Brief-BESTest) and the clinical parameters (ASMMI, CSA, IMAT_rel, and IMAT_abs) was tested by the Pearson’s correlation index while data homogeneity between sarcopenic and nonsarcopenic subjects was tested through unpaired Student <i>t</i> tests or with the Mann-Whitney rank test. Effect sizes (ES) were used to determine the magnitude of the effect for all significant outcomes. <b><i>Results:</i></b> Eleven subjects were classified as sarcopenic and 18 as nonsarcopenic based on their ASMMI (cutoff value: 5.5 kg/m²). A positive correlation between OAK and CSA was observed (<i>r</i>² = 0.19; <i>p</i> = 0.033), whereas a negative correlation between OAK and IMAT_rel was detected (<i>r</i>² = 0.27; <i>p</i> = 0.009). No correlations were observed between OAK and ASMMI and between ASMMI and IMAT_rel. Sarcopenic subjects showed significantly lower weight (<i>p</i> = 0.002; ES = 1.30, large), BMI (<i>p</i> = 0.0003; ES = 1.82, large), CSA (<i>p</i> = 0.010; ES = 1.17, moderate), and IMAT_abs (<i>p</i> = 0.022; ES = 1.63, large) than nonsarcopenic individuals, whereas OAK scores and IMAT_rel were similar between groups. <b><i>Discussion/Conclusion:</i></b> Increased IMAT and lower CSA in the thigh muscles are associated with higher risk of fall while ASMMI, a value of appendicular muscle mass, was not associated with physical performance in older adults.

**背景（Background）：** 骨骼肌的数量与组成和老年人身体功能衰退之间的关联目前尚不明晰。本交叉研究的首要目的是探讨绝经后骨质疏松老年女性的大腿肌间脂肪组织（intermuscular adipose tissue, IMAT）浸润情况、四肢肌肉量与跌倒风险之间的关联。其次，本研究基于双能X线吸收测定法（dual-energy X-ray absorptiometry, DXA）计算的四肢骨骼肌质量指数（Appendicular Skeletal Muscle Mass Index, ASMMI）将老年受试者分为少肌症（sarcopenic）组与非少肌症（nonsarcopenic）组，进而分析同一队列在肌肉量、IMAT及跌倒风险方面的组间差异。
**方法（Methods）：** 本研究共纳入29名受试者（年龄：72.4±6.8岁；身体质量指数（Body Mass Index, BMI）：23.0±3.3；T值：-2.7±0.2），完成以下临床评估：(1) 全身DXA扫描以测定ASMMI；(2) 磁共振成像检测大腿肌肉的横截面积（cross-sectional muscle area, CSA）与IMAT，分别以绝对量（IMAT_abs）和相对量（IMAT_rel）表示；(3) 通过OAK系统（Khymeia公司，意大利诺文塔帕多瓦纳）进行跌倒风险评估。采用皮尔逊相关系数检验跌倒风险（OAK评分，即简明BESTest量表的自动化版本）与各项临床指标（ASMMI、CSA、IMAT_rel及IMAT_abs）之间的相关性；采用独立样本t检验或曼-惠特尼秩和检验比较少肌症组与非少肌症组的组间数据齐性。针对所有具有统计学意义的结局指标，采用效应量（Effect Sizes, ES）分析其效应幅度。
**结果（Results）：** 根据ASMMI的截断值5.5 kg/m²，共11名受试者被归类为少肌症组，18名为非少肌症组。研究观察到OAK评分与CSA呈正相关（r²=0.19；P=0.033），而OAK评分与IMAT_rel呈负相关（r²=0.27；P=0.009）；未发现OAK评分与ASMMI之间、以及ASMMI与IMAT_rel之间存在相关性。与非少肌症组受试者相比，少肌症组受试者的体质量（P=0.002；ES=1.30，大效应）、BMI（P=0.0003；ES=1.82，大效应）、CSA（P=0.010；ES=1.17，中等效应）及IMAT_abs（P=0.022；ES=1.63，大效应）均显著更低，而两组间的OAK评分与IMAT_rel无显著差异。
**讨论/结论（Discussion/Conclusion）：** 大腿肌肉的IMAT升高与CSA降低均与更高的跌倒风险相关；而作为四肢肌肉量指标的ASMMI，则与老年人的身体机能表现无显著关联。