Identifying Individuals at Risk of Functional Decline Despite Preserved Muscle Mass: Insights from Appendicular Skeletal Muscle Mass and Handgrip Strength Discordance

Background: Muscle strength is a more robust indicator of functional health than muscle mass alone, yet muscle mass-based assessments remain common. Discordance between appendicular skeletal muscle mass (ASM) and handgrip strength (HGS) reflects impaired muscle quality and may identify individuals at risk of functional decline despite preserved muscle mass. Methods: We conducted a cross-sectional analysis of adults aged >18 years from the KNHANES 2022–2023 (N = 4130). Mean ages were 57.7 ± 17.2 years in men and 58.4 ± 16.3 years in women. ASM was measured by bioelectrical impedance analysis and HGS using a standardized dynamometer. ASM–HGS discordance was defined as the residual difference between observed and predicted HGS. Sex-stratified, survey-weighted linear regression models were used to identify associated factors, with dose–response relationships examined across quintiles of age and body fat percentage. Results: ASM and HGS were moderately correlated in both men (PCC = 0.615) and women (PCC = 0.567), with substantial interindividual discordance. Greater ASM-HGS discordance was independently associated with older age and higher body fat percentage in both sexes, demonstrating clear dose–response relationships, with progressively greater muscle mass-dominant patterns at higher levels of age and adiposity. Anemia was independently associated with greater discordance in both men and women, with a significant interaction by sex. Conclusions: Although ASM and HGS are strongly correlated in Korean adults, clinically meaningful discordance exists in a substantial subset, revealing heterogeneity in muscle quality not captured by muscle mass alone. Excess adiposity and aging are major determinants of this discordance.