To explore the dose-response correlation between appendicular skeletal muscle index (ASMI) and muscle strength in older adults.

This study included adults aged 60-79 years from the 2024 National Routine Physical Fitness Surveillance database. ASMI was used to assess muscle mass, while handgrip strength and 30-second chair stand test (30-s CST) repetitions were employed to evaluate muscle strength. Linear regression analyses, adjusted for age and body mass index (BMI), were performed to examine the associations between ASMI and handgrip strength/30-s CST. Additionally, restricted cubic spline (RCS) models were applied for dose-response analysis.

A total of 68 038 older adults (56.3% female, mean age 68.0±5.4 years) were included. Males exhibited significantly higher handgrip strength(33.6± 7.8 kg vs. 23.4±5.6 kg, P < 0.001) and ASMI (13.6±1.3 kg/m² vs. 11.4±1.2 kg/m², P < 0.001) than females. Linear regression revealed significant positive associations between ASMI and both handgrip strength(β=0.940, 95% CI: 0.930-0.950, P < 0.001) and 30-s CST repetitions(β=0.008, 95% CI: 0.005-0.011, P < 0.001), with consistent trends across genders. RCS analysis identified a threshold effect of ASMI on handgrip strength in older men (cut-off: 13.55 kg/m², P < 0.001), but not on 30-s CST(P=0.090). In women, significant thresholds were observed for both handgrip strength and 30-s CST(cut-off: 11.25 kg/m², P < 0.001). Below these thresholds, muscle strength declined rapidly with decreasing ASMI.

s Muscle mass and strength are significantly positively correlated in older adults. Personalized muscle health interventions should be considered to reduce the rate of decline in muscle strength, when ASMI falls below 13.55 kg/m² in men or 11.25 kg/m² in women.