Low muscle function and obesity defined by handgrip strength or sit-to-stand performance in relation to depressive symptoms and cognitive impairment in Korean older adults

Background: Low muscle function and obesity often coexist in later life, but this combined phenotype is usually defined by handgrip strength (HGS) alone. Whether an upper-extremity strength test and a lower-extremity performance test show comparable associations with depressive symptoms and cognitive impairment is unclear. Methods: This exploratory cross-sectional study included 938 community-dwelling Korean older adults aged 65 years or older. Low HGS followed the 2019 Asian Working Group for Sarcopenia criteria, low 30-second sit-to-stand (30-s STS) performance was the sex-specific lowest quartile, and obesity was a body mass index ≥ 25 kg/m². Participants were cross-classified into normal, low-muscle-function-only, obesity-only, and combined groups. Logistic regression was adjusted for age, sex, education, living alone, physical activity, and medications, and interaction was tested on multiplicative and additive scales. Results: Relative to the normal group, the combined HGS-based group was associated with depressive symptoms (odds ratio 4.18, 95% confidence interval 2.29-7.62) and cognitive impairment (2.58, 1.53-4.37); 30-s STS-based estimates were 2.99 and 1.89. The combined groups did not differ from the low-muscle-function-only groups (all p > 0.5), and no interaction was significant. Discriminative ability was similar for the two tests. Conclusion: Low muscle function rather than its combination with obesity was the dominant correlate of depressive symptoms and cognitive impairment. These exploratory associations require longitudinal confirmation.