Within-day and between-day reliability of thickness measurements of abdominal muscles using ultrasound during abdominal hollowing and bracing maneuvers

Ultrasonography imaging has been used as a non-invasive method to estimate the thickness and relative activities of the abdominal muscles in patients with lower back pain (LBP). However, the statistical reliability of US thickness measurements of abdominal muscles, including transversus abdominis (TrA), internal oblique (IO) and external oblique (EO) muscles during abdominal hollowing (AH) and abdominal bracing (AB) maneuvers has not been well-investigated. This study was performed on a total of 20 female subjects (10 with LBP and 10 without LBP) in the age range of 25-55 years to assess within-day and between-day reliability of the measurements. US measurements on maneuvers were repeated after two hours for the within-day reliability and after five days for the between-day reliability assessment. High intra-class correlation coefficient (ICC) values (>0.75) for within-day and between-day reliability assessments during AH maneuver were concluded. The ICC values were moderate for reliability assessment during AB. The ICC values for AH were greater than AB both for within- and between-day reliabilities. The small standard error of measurement and minimal detectable change values (0.16-0.78 and 0.44 to 2.15, respectively) were found for both AH and AB. We recommend real-time US imaging as a reliable way of determining the thicknesses of the TrA and IO muscle (and to some extent, EO muscle) for both healthy and LBP patients.