What really matters mobility of middle-aged and older adults: low muscle mass or obesity?

Study objective: This study explored which body size–adjusted skeletal muscle indices (SMI) has a better correlation with mobility and cardiometabolic health. Additionally, the roles of low muscle mass and obesity in the mobility and cardiometabolic health of individuals were identified. We hypothesized that body mass index (BMI)-or body weight (Wt)-adjusted SMI had a better correlation with mobility in middle-aged and older adults with obesity than did body height (Ht)-adjusted SMI. Methods: 427 community-dwelling middle-aged and older adults (age: 66.0±9.0 years) underwent assessments of body composition (dual-energy X-ray absorptiometry and waist circumference [WC]), grip strength, and mobility (timed up-and-go test and chair stand test). WC was used as a surrogate for obesity. Chi-square test and one-way analysis of variance were used to compare grip strength, mobility, and cardiometabolic health among individuals with normal body composition (N), only low muscle mass (S), only obesity (O), and low muscle mass plus obesity (SO). Pearson’s correlation coefficient was used to examine the correlation between muscle strength/mobility and different body size–adjusted SMI. Regression models were used to examine the factors independently associated with muscle strength, mobility, and cardiometabolic health. The significance level was set at α<0.05. Results: The O group, but not the S group, had poorer mobility than the N group, regardless of the SMI used to define low muscle mass. The O and SO groups had a higher prevalence of cardiometabolic diseases. The relationship between muscle mass and mobility existed in individuals with obesity, but not in individuals without obesity. After adjusting for age, sex, and WC, ASM/BMI was the only SMI that was correlated with grip strength. Similarly, only ASM/BMI was positively correlated with performance on the timed up-and-go test in the population with obesity (p<0.05). When age and sex were controlled, WC, but not SMI (regardless of adjusting for Ht, Wt, or BMI), was associated with mobility and cardiometabolic health. Conclusion: BMI-adjusted SMI had a better correlation with mobility in middle-aged and older adults with obesity than did Ht- and Wt-adjusted SMI. Obesity plays a more independent role in mobility and cardiometabolic health than low muscle mass in middle-aged and older adults. This study was supported by the Ministry of Science and Technology, Taiwan This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.