Reliability of ultrasonography for transversus abdominis and lumbar multifidus thickness in participants with and without low back pain

Objective To evaluate the reliability of the transversus abdominis (TrA) and lumbar multifidus (LM) muscle assessment through musculoskeletal ultrasound (MSU) by exploring changes in the muscle thickness across the rest, contraction, and respiratory cycle (RC) phases in both nonspecific low back pain (NSLBP) participants and healthy participants. Methods This study recruited 32 participants between the ages of 20 and 50 both with and without NSLBP. Two raters measured images of the TrA and LM muscles using MSU; measurements were recorded at rest, during contraction, and throughout phases of the RC. Whereas the absolute dependability was assessed using the standard error of measurement (SEM) and minimal detectable change (MDC), the reliability analysis used intraclass correlation coefficients (ICCs). Results MSU showed good to excellent intra- and inter-rater reliability in terms of assessing TrA and LM muscle thickness, with ICC scores varying between 0.773 and 0.998. SEM and MDC values suggested satisfactory reliability and low variability of measurements. The reliability measures were comparable in all breathing cycles and states of contraction in both healthy participants and participants with NSLBP. Conclusions The inter-rater and intra-rater reliability of the MSU for assessing TrA and LM thickness at rest and contraction during different phases of the RC in participants with and without NSLBP indicates consistent and reliable measurements.