Analysis of the relationship between the transversus abdominis and lower back pain using an ultrasound

[Purpose] This study aimed to observe the thickness of the transverse abdominis muscle in different contraction states using ultrasound, and to investigate the diagnostic capability of transverse abdominal muscle thickness for nonspecific lower back pain. [Participants and Methods] This study included 108 healthy adults (30–50 years old), consisting of 33 participants with low back pain (13 males, 20 females; defined as those who had experienced low back pain for more than six months) and 75 participants without low back pain (22 males, 53 females). The body mass index, body trunk muscle mass, and transverse abdominal muscle thickness, measured at a static state, during the end of inspiration, end of expiration, transverse abdominis contraction, and simultaneous pelvic floor and transverse abdominis muscle contraction, were measured. [Results] Chronic low back pain was correlated with the transverse abdominis muscle thickness during simultaneous transverse abdominis and pelvic floor muscle contraction. [Conclusion] The thickness of the transverse abdominis muscle during simultaneous transverse abdominis and pelvic floor muscle contraction was a viable diagnostic index for evaluating the degree of chronic lower back pain.