Intra-rater reliability of measurement of abdominal perimuscular connective tissue thickness on ultrasound images

[Purpose] The thickness of the perimuscular connective tissue (PMCT) reflects muscular atrophy and decreased flexibility that may cause low back pain. However, few studies have used ultrasound imaging to measure PMCT thickness. We aimed to examine and confirm the reliability of ultrasound in measuring the thickness of the PMCT of the abdominal wall muscle. [Participants and Methods] The participants were 38 healthy adult males without chronic back pain. The images were acquired in B mode with the participants in the supine position and the PMCT thickness of the abdominal wall muscle was measured on the images. The intraclass correlation coefficient (ICC) was used to confirm reliability. [Results] The ICC for both within-day and between-day PMCT measurements by ultrasound were 0.7–0.9. The 95% confidence interval ranged from 0.5–0.9. The standard error of measurement (SEM) was 0.02–0.1 mm in the abdominal wall muscle and 0.5 mm in the interrecti distance (IRD). The 95% confidence interval (95% CI) of the minimum detectable change (MDC95) was 0.1–0.3 mm in the abdominal wall muscle and 1.3–1.4 mm in the IRD. [Conclusion] We conducted a study to confirm the reliability of ultrasound-based measurement of PMCT thickness of the abdominal wall muscle, and the ICC results established reliability. However, since the values measured were small (0.02–1.4 mm) and there is a limit to visual observation, it was necessary to measure using computer software.