Age-Related Structural-Functional Discrepancy in Muscle Indicators Among Rural Korean Older Women

Age-related loss of muscle mass and function contributes to mobility limitations, loss of independence, and other adverse health outcomes. Structural and functional indicators characterize muscle health but may not change in parallel with advancing age. Evidence from rural populations remains limited. This study aimed to examine age-related differences in structural and functional muscle indicators among rural community-dwelling women and to determine whether age-group differences are greater in functional than in structural indicators.

This cross-sectional study included 211 community-dwelling women aged 50-89 years residing in rural Asan, Korea. Participants were categorized into four age groups (50-59, 60-69, 70-79, and 80-89 years). Structural indicators included skeletal muscle index (SMI), skeletal muscle mass (SMM), thigh circumference (TC), and calf circumference (CF). Functional indicators included handgrip (HG) strength, isometric knee extensor (KE) strength, and the five-times sit-to-stand test (5×STS). Between-group differences were analyzed using one-way analysis of variance (ANOVA), and domain-level differences were further examined using a mixed-design repeated-measures ANOVA. To facilitate comparison across indicators, variables were normalized to the 50-59 age group (set to 100).

Structural and functional indicators showed different magnitudes of age-related change across groups. HG and KE were lower in older groups and showed larger between-group differences than the structural indicators. In contrast, 5×STS time increased across age groups, from 7.0 ± 1.75 s in the 50-59 group to 15.2 ± 6.60 s in the 80-89 group. Relative SMI decreased to 81.5% of the reference group, whereas the relative index for 5×STS (reciprocal time) decreased to 46.0% (all p < 0.001).

Structural and functional muscle indicators showed divergent age-related patterns among rural community-dwelling women. The performance-based 5×STS demonstrated substantially greater relative differences than structural indicators, supporting the inclusion of functional assessments alongside structural measures for age-stratified evaluation in rural settings.