Effects of arm and leg positions on lumbar multifidus muscle activity while on hands and knees or while standing.

Background: The lumbar multifidus (LMF) muscle, which is involved in the mechanical stability of the lumbar spine, reportedly undergoes atrophy in patients with low back pain. Preventing or mitigating low back pain requires strengthening the LMF muscle; however, methods for triggering selective and significant contraction of this muscle have not been fully studied. This study aims to clarify how, in the hands-and-knees or standing position, the position of the arm and leg on one side affects the activity of the lumbar erector spinae (LES) and LMF muscles.