Ultrasound measurement of deep abdominal muscle activity in sitting positions with different stability levels in subjects with and without chronic low back pain.

The purpose of this study was to investigate the changes in the thickness of the transversus abdominis (TrA) and internal oblique (IO) muscles in three sitting postures with different levels of stability. The technique of ultrasound imaging was used for individuals with and without chronic low back pain (LBP). A sample of 40 people participated in this study. Subjects were categorised into two groups: with LBP (N = 20) and without LBP (N = 20). Changes in the thickness of tested muscles were normalized under three different sitting postures to actual muscle thickness at rest in the supine lying position and were expressed as a percentage of thickness change. The percentage of thickness change in TrA and IO increased as the stability of the sitting position decreased in both groups. However, the percentages of thickness change in all positions were less in subjects with LBP. There was a significant difference in thickness change in TrA when sitting on a gym ball between subjects with and without LBP but no difference was found when sitting on a chair. There was no significant difference in thickness change in IO in all positions between the two groups. Our findings indicate that difference in the percentage of thickness change in TrA between subjects with and without LBP increases as the stability of sitting position decreases.