Muscle Mass Adjusted by Body Height is not Correlated with Mobility of Middle-Aged and Older Adults

Background: Low muscle mass and obesity are associated with mobility disability, cardiometabolic diseases, and loss of independence. Three skeletal muscle indices (SMIs) are proposed to adjust the body size of individuals. However, it is unknown which index is better correlated with mobility. Additionally, it remains unclear whether low muscle mass or abdominal obesity has a greater impact on the mobility and cardiometabolic health of older adults. Objectives: This study explored the association between different SMIs {appendicular skeletal muscle mass [ASM] adjusted by body height [Ht], body weight [Wt], or body mass index [BMI (kg/m2)]} and mobility/cardiometabolic health. The roles of low muscle mass and abdominal obesity in the mobility and cardiometabolic health of individuals were also identified. Methods: Four-hundred and twenty-seven community-dwelling middle-aged and older adults underwent body composition assessments [dual-energy x-ray absorptiometry and waist circumference (WC)], grip strength, and mobility (timed up-and-go test and chair stand test). Spearman's rank correlation coefficient and regression models were used to examine research questions. This study was registered in the Thai Clinical Trials Registry (registration number: TCTR20210521007). Results: All SMIs were positively correlated with the grip strength (ASM/Ht2: r = 0.392; ASM/Wt: r = 0.439; ASM/BMI: r = 0.569). Regarding mobility, only ASM/Ht2 wasn't relevant. After adjusting for age, sex, and WC, ASM/BMI was the only SMI associated with grip strength (β = 0.274). When age and sex were controlled, WC, but not SMI, was associated with mobility and cardiometabolic health. Conclusions: ASM/Ht2 did not correlate with mobility in middle-aged and older adults, whereas ASM/Wt and ASM/BMI did. Abdominal obesity has a greater impact on mobility and cardiometabolic health than low muscle mass in middle-aged and older adults. We recommend using ASM/BMI to identify the low muscle mass of individuals. In addition, clinicians should note the important role of abdominal obesity when considering mobility in middle-aged and older adults.