The Intra-Rater Reliability of Ultrasonography for the Measurement of Lumbar Multifidus and Erector Spinae Thickness in Different Positions in People with and without Active Extension-Related Non-Specific Low Back Pain.

The paraspinal muscles, including multifidus (MF) and erector spinae (ES) play key roles in the stability and movement of the lumbar spine. This study aimed to determine the intra-rater reliability of the ES and MF muscle thickness measures of the rehabilitative ultrasound imaging (RUSI) in people with active extension pattern (AEP) non-specific chronic low back pain and controls.