Differences in Transversus Abdominis Muscle Function between Chronic Low Back Pain Patients and Healthy Subjects at Maximum Expiration: Measurement with Real-time Ultrasonography

[Purpose] The purpose of the present study was to compare the contraction ability at maximum expiration of the transversus abdominis (TrA) in patients with chronic low-back pain (CLBP) with that of healthy individuals. [Subjects] We studied 15 patients with CLBP and 15 healthy subjects. The subjects were informed of the study's aim and methods, and the experiment was performed after obtaining the consent of the subjects. [Methods] The thickness of the abdominal muscles was measured using a LOGIQ Book XP (GE, USA). The main outcome variable was the ratio of TrA thickness at maximum expiration versus in the relaxed position (TrA activation ratio). [Results] There was a difference between the healthy subjects and the back pain subjects with regard to the thickness of the TrA at rest and the thickness of the muscle during contraction. However, there was no difference in the rate of change in the muscle activity. [Conclusion] In conclusion, CLBP patients exhibited atrophy of the TrA muscle, but voluntary TrA muscle activation was similar to that of the normal subjects. Key words: Low back pain, Transversus abdominis, Maximum expiration