Physical characteristics correlated with echo intensity of the lumbar multifidus in community-dwelling elderly women: A cross-sectional study

Ultrasound echo intensity (EI), a widely used indicator of skeletal muscle quality, is associated with physical performance and muscle strength. However, evidence regarding the relationship between lumbar multifidus EI and muscle oxygenation or hemodynamic characteristics in older adults is limited. This cross-sectional study included 34 community-dwelling older women. The EI of the lumbar multifidus muscle was measured using ultrasonography. Hemodynamic parameters were assessed using near-infrared spectroscopy during prone, sitting, standing, walking, and post-walk standing. Walking speed, spinal sagittal alignment, and body composition were evaluated. Spearman’s correlation analysis examined associations between EI and measured variables. Partial correlation and multiple linear regression analyses were additionally conducted for variables significantly associated with EI. In the complete-sample analysis, EI was significantly correlated with oxy[Hb+Mb] during post-walk standing. Sensitivity analyses excluding one influential observation confirmed the association remained significant after adjustment for age, body mass index, and subcutaneous fat thickness. Multiple linear regression analysis also identified oxy[Hb+Mb] as an independent factor associated with EI. No significant associations were observed between EI and age, body composition variables, spinal alignment parameters, walking speed, or the remaining hemodynamic variables. A relationship between lumbar multifidus EI and post-walk oxy[Hb+Mb] was observed in community-dwelling older women. These exploratory findings suggest that EI may reflect muscle oxygenation physiological characteristics in addition to morphological muscle quality; however, the underlying physiological mechanisms remain unclear. This association was observed in the complete-sample analysis, although strength was influenced by an influential observation. Therefore, the findings should be interpreted cautiously and confirmed in larger, prospective studies.