• I-Shan Liu, Huei-Ming Chai, Jing-Lan Yang, and Shwu-Fen Wang.
• Division of Physical Therapy, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan.
• Man Ther. 2013 Dec 1;18(6):481-6.

Study DesignReliability study.ObjectiveTo investigate the inter-session reliability of measuring the thickness of deep (dMF) and superficial layer of lumbar multifidus (sMF) using ultrasonography for participants with and without low back pain (LBP).BackgroundThe lumbar multifidus is an important muscle in maintaining spinal stability. The dMF is considered important in maintaining tonic contraction and joint stability. Motor control impairment is also discovered in patients with LBP. However, no study to date has investigated the method of observing both the sMF and dMF through ultrasound imaging (USI).MethodsTwenty subjects aged 18-35 years old with LBP (N=10) and without LBP (N=10) were recruited. Every subject extended the upper trunk in prone lying with maximal isometric contraction. Simultaneously, the examiner measured the thickness of the dMF and the sMF using ultrasonography after ensuring the muscle belly was located. The participants performed three trials of isometric trunk extension in each session, with 30 min between each session. The reliability of measuring the change of thickness is represented by the intra-class correlation coefficient (ICC).ResultsThrough averaging three trials of measurement, the reliability of measuring the thickness of the dMF or the sMF in static or in the contracted condition, and the change of the thickness during contraction, is reliable (ICC=0.84-1.00).ConclusionsThe intra-rater inter-session reliability of measurement of the dMF and the sMF with USI has been established. This method could be applied to the qualification of the activation level of the dMF and the sMF with specific tasks.Copyright © 2013 Elsevier Ltd. All rights reserved.

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