Combined B-mode ultrasonography and shear-wave elastography protocol for lower-limb musculo-tendinous properties assessment: A pilot investigation of test-retest reliability in recreational athletes.

Evaluating the test-retest reliability of shear-wave elastography (SWE) is essential to interpret changes observed in clinical or sports science studies that employ pre/post intervention designs or longitudinal monitoring of musculoskeletal adaptations and pathologies. A simple, standardized protocol using only an ultrasound device to assess both the morphological and mechanical properties of the lower limbs has been described. The main purpose of this exploratory study was to assess reliability of SWE for measuring muscles and tendons' elasticity of knee extensors and plantar flexors. Reliability of B-mode ultrasound (US) in measuring tendons' morphological characteristics (length, thickness, and cross-sectional area) was also assessed. The protocol was administered to recreational athletes on three occasions by the same examiner, with the first two sessions separated by a 30-min interval (within-day reliability) and the third session scheduled 24 h after the first one (between-day reliability). Morphological parameters demonstrated excellent reliability, with Intraclass Correlation Coefficients (ICCs) ranging from 0.92 to 0.99 and relative Standard Error of Measurement (SEM) less than 5%. For tendons' and muscles' elasticity, reliability was more uncertain. Muscle shear-wave velocity showed acceptable ICC estimates (0.76-0.91) for most plantar flexor and knee extensor muscles although the width of confidence intervals and the magnitude of Minimal Detectable Change (MDC) for some SWE outcomes limits the generalizability of the findings. Poor reliability was found for gastrocnemius medialis and vastus medialis.