A comparison of abdominal muscle thickness changes after a lifting task in subjects with and without chronic low-back pain.

Objective: Using ultrasound imaging, the abdominal muscles' response to the back extensor muscle fatigue was assessed in subjects with chronic low-back pain (CLBP).

Background: Lumbar muscle fatigue is a common occurrence among workers. Alteration in motor coordination is one consequence of muscular fatigue. According to previous studies, CLBP subjects use their back and abdominal muscles in different ways, but questions remain about abdominal muscle responses to back muscle fatigue in CLBP patients.

Method: Thirteen CLBP patients and 15 healthy subjects participated in this study. The thickness of abdominal muscles-including transverse abdominis (TrA), internal oblique abdominis (IO), and external oblique abdominis (EO) muscles-was measured in standing position with and without axial loads before and after a lifting fatigue task.

Results: The results reveal a significant difference for the main effects of group on percentage of change in TrA thickness (F = 8.9, p = .004). Percentage of change in thickness of TrA was 10% greater in the CLBP group. Although IO thickness displayed greater percentage of change in the CLBP group, the difference between groups was not significant.

Conclusion: Abdominal muscle behavior changes with back-muscle fatigue in both healthy and CLBP subjects, but responses were more exaggerated in CLBP patients.

Application: Ultrasound imaging technique can provide critical information about the effect of fatigue on spinal muscle activation and consequently about the stability of the spine. As a more applicable and easy technique, ergonomists can use ultrasound imaging in musculoskeletal system assessment in worker populations in future studies.