Reliability of ultrasound measurement for isolated control of the transversus abdominis muscle during abdominal hollowing: A secondary analysis.

Ultrasonography (US) measurements of the transversus abdominis muscle (TrA) during abdominal hollowing (AH) are conducted at the maximum AH, which would be unable to evaluate isolated control of the TrA to the internal or external oblique muscles (outer muscles). The present study aimed to establish a reliable method to evaluate the skills of isolated control of the TrA to the outer muscles using US. The datasets of two follow-ups were analyzed with 1-week interval of a wait-and-see control group comprising 20 participants with LBP in a randomized controlled trial. The primary measures were; % change in the thickness of the TrA at 1 cm lateral to the muscle-fascia junction of the TrA, and changes in horizontal distance of the superior edge of the TrA fascia. The measurement time points were immediately before AH during resting and when outer muscle thickness above 1 cm lateral to the muscle-fascia junction of the TrA increased by 10%. Consequently, five repetitions were required to obtain a stable mean value and good reliability (intraclass correlation coefficient [ICC] = 0.65-0.68 for the % change, and 0.84-0.88 for the change in horizontal distance; ICC = 0.82 for the % change, and 0.93 for the change in horizontal distance).