Establishment and efficacy validation of sex-age-specific diagnostic cutoffs for sarcopenia: targeting the decline inflection points of muscle health indicators in community-dwelling middle-aged and elderly

Background: Sarcopenia is an age-related condition, with existing international guidelines predominantly focusing on the elderly and lacking age-specific diagnostic criteria. This study aims to investigate the prevalence of sarcopenia among middle-aged and elderly individuals in the Community, establish reference standards for muscle health indicators stratifiedby gender and age, and analyse age-related patterns of change and the validity of diagnostic cut-offs. Methods: A cross-sectional design was employed. Between April and June 2025, 2, 631 subjects aged ≥35 years from a community in Shijiazhuang, China, were enrolled and divided into sex-specific subgroups: 35-49, 50-64, and ≥65 years. Muscle Index (SMI), grip strength, and gait speed were measured. Diagnosis was based on the AWGS 2019 criteria. Stratified cutoffs were established using the P20 method, decline inflection points analysed via LOESS, and efficacy validated through ROC curves. Results: Overall sarcopenia prevalence was 6.65% (8.44% in males, 4.75% in females), rising to 15.26% in the ≥65 age group. Muscle indicators exhibited non-linear age-related decline with sex-specific inflection points; P20 cut-off decreased with age. AUC values for all indicators exceeded 0.75 in both the 50-64 and ≥65 age groups, demonstrating sound diagnostic performance. Conclusion: This study established sex and age stratified diagnostic cut-offs for sarcopenia in community-dwelling middle-aged and elderly individuals, elucidated the decline characteristics of core muscle indicators, and provided evidence for stratified community screening and precise prevention and control. It aligns with the concept of lifelong muscle health management and offers theoretical support for age-specific interventions.