Association between knee extensor muscle strength and locomotive syndrome in adults undergoing health screening: A cross-sectional study

BACKGROUND: Locomotive syndrome is characterized by reduced mobility due to musculoskeletal impairment and is associated with an increased risk of disability and long-term care needs. Although knee extensor muscle strength is essential for mobility, its independent association with locomotive syndrome in health screening populations remains unclear. METHODS: This cross-sectional study included adults undergoing routine comprehensive health check-ups at a preventive medical center between 2016 and 2023. Locomotive syndrome was defined according to the Japanese Orthopaedic Association criteria using the stand-up test, two-step test, and 25-question Geriatric Locomotive Function Scale. Multivariable logistic regression analyses were conducted to examine the association between knee extensor muscle strength and locomotive syndrome, after adjusting for age, sex, year of measurement, body mass index, and skeletal muscle index. Secondary analyses evaluated associations with individual locomotive syndrome components. RESULTS: A total of 2652 participants were included, of whom 1061 (40.0%) had locomotive syndrome. Higher knee extensor muscle strength was independently associated with lower odds of locomotive syndrome (odds ratio [OR] per 1 SD increase: 0.576; 95% confidence interval [CI]: 0.522-0.636; p < 0.001). This association remained significant in both age groups (<65 and ≥ 65 years). In secondary analyses, knee extensor muscle strength was significantly associated with all locomotive syndrome components, with stronger associations for the two-step test (OR: 0.417; 95% CI: 0.354-0.492) and stand-up test (OR: 0.459; 95% CI: 0.405-0.520) than for the 25-question Geriatric Locomotive Function Scale (OR: 0.787; 95% CI: 0.710-0.873) (all p < 0.001). CONCLUSIONS: Lower knee extensor muscle strength was independently associated with locomotive syndrome in adults undergoing health screening, particularly for performance-based components. Assessment of knee extensor muscle strength may provide complementary information for musculoskeletal functional evaluation in health-screening settings.