Reliability of transversus abdominis and gluteus medius muscle thickness measurements using ultrasound imaging in chronic non-specific low back pain individuals

Transversus abdominis (TrA) and gluteus medius (GM) play important roles as primary stabilizers of the lumbopelvic-hip complex. Dysfunction of these muscles has been associated with low back pain (LBP), which affects lumbopelvic stability. This study aimed to evaluate the intra-rater and inter-rater reliability of the TrA and GM muscle thickness during standing and single-leg standing, both with and without the abdominal drawing-in maneuver (ADIM). A total of 24 participants, 12 asymptomatic and 12 with non-specific low back pain (NSLBP), were enrolled. Muscle thickness was determined as the average of three consecutive measurements. Intraclass correlation coefficients (ICC) were used to assess reliability, and the standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated. The results demonstrated high intra-rater reliability for the TrA (0.86-0.98) and the GM (0.90-0.99), and high inter-rater reliability for the TrA (0.86-0.95) and the GM (0.91-0.99). The SEM for TrA ranged from 0.12 to 0.39 and the GM ranged from 0.63 to 1.83, while the MDC for TrA ranged from 0.35 to 1.09 and for GM ranged from 1.75 to 5.08 mm. The thickness measurement of the TrA and GM muscles demonstrated high reliability and clinical applicability in both standing and single-leg standing positions.