Inter- and intra-rater reliability of ultrasound-derived muscle quantification

Ultrasound devices are now commonplace in sports medicine facilities due to their ease of use and validity to assess skeletal muscle characteristics. The aim of the current study was to assess the reliability of ultrasound skeletal muscle image analysis across multiple raters. Vastus lateralis (VL), rectus femoris (RF), and first dorsal interosseus (FDI) images were analyzed in ImageJ by three raters to determine muscle thickness (MT), cross-sectional area (CSA), and echo-intensity (EI). Intra-class correlation coefficients (ICC) between (inter-rater) and within (intra-rater) raters, the standard error of the measurement (SEM) and minimal difference needed to be considered real (MD) were calculated. Inter-rater reliability was high for the selected outcomes of the VL and RF (ICC: 0.987–0.999), while the FDI was lower (0.614–0.962). The MD was small in each muscle and outcome. Intra-rater reliability ranged from 0.961–0.999 for all three raters of differing experience with ImageJ. Providing specific directions to analyze ultrasound images results in reliable ultrasound measurements for the FDI, RF, and VL. The FDI may have had lower ICCs due to the uneven nature and borders. Future studies should continue to investigate the reliability of ultrasound measurements across more raters, various skeletal muscles, and independently per lab group.