Ultrasound-derived muscle variables and physical function in older adults: A scoping review

Background: Evidence on use of ultrasound to assess muscles in older adults, and its relation to clinically relevant measures is diverse and inconsistent. Objective: To map and synthesize evidence on use of ultrasound-derived muscle variables and their associations with measures of physical function in older adults. Methods: A scoping review was conducted in accordance with PRISMA-ScR and JBI guidance. MEDLINE, Cochrane, Embase, Scopus, CINAHL, and grey literature was searched. Eligible studies included adults ≥65 years, including frail cohorts, reporting association between ultrasound-derived muscle variables (muscle thickness (MT), cross-sectional area (CSA), echo intensity (EI), pennation angle (PA), fascicle length (FL), or shear-wave elastography (SWE)) and physical function measures (handgrip strength (HGS), sit-to-stand (STS), gait speed (GS), timed up-and-go (TUG), or short physical performance battery (SPPB)). Results: Seventy studies met inclusion criteria. Mapping revealed that rectus femoris MT at mid-thigh was most frequently examined, with considerable protocol variation. Most studies used cross-sectional designs, and frail cohorts were underrepresented. MT and CSA showed weak to moderate associations with muscle strength-related measures (HGS and STS) and generally very weak to weak associations with physical performance-related measures (GS, TUG, SPPB). Evidence for EI, SWE, PA, and FL was limited and inconsistent. Conclusion: Current evidence provides limited support for ultrasound-derived muscle variables as markers of physical function in older adults. Muscle thickness and cross-sectional area capture aspects of muscle strength but insufficiently reflect physical performance. Establishing harmonized protocols and exploring responsiveness in frail populations, in longitudinal studies are critical steps for future research and clinical application.