Automatic activity of deep and superficial abdominal muscles during stable and unstable sitting positions in individuals with chronic low back pain

Objective The purpose of this study was to assess muscle thickness changes in the deep and superficial abdominal muscles, during sitting on stable and unstable surfaces in subjects with and without chronic low back pain (CLBP). Method A cross-sectional study was conducted involving 40 participants (20 CLBP and 20 healthy). Ultrasound imaging was used to assess changes in the thickness of the Transversus abdominis (TrA), Internal Oblique (IO), Rectus abdominis (RA) and External oblique (EO) muscles. Muscle thickness under two different sitting postures; (sitting on a chair and sitting on a Swiss ball), was normalized to actual muscle thickness at rest in the supine lying position and was expressed as a percentage of thickness change of muscles. Result The results showed significantly greater thickness changes in RA muscle in the CLBP patients compared to the healthy subjects, during both stable and unstable sitting positions. Also, significantly lower thickness changes in TrA muscle was observed in subjects with CLBP compared to those without CLBP, during unstable sitting position. Conclusion There was an imbalance between the automatic activity of TrA and RA muscles in the subjects with CLBP, compared to the pain-free controls, during an unstable sitting position. Therefore, it is necessary to pay attention, to the altered automatic activity of the abdominal muscles while utilizing a Swiss ball, for rehabilitation of subjects with CLBP.