Recent research on lumbar musculature and how it relates to individuals suffering from lower back pain has progressed through the use of advanced imaging techniques. Dangeria and Naesh28 conducted a clinical prospective cohort study examining the cross-sectional area of the psoas major in healthy volunteers and subjects with unilateral sciatica caused by a disc herniation. These authors demonstrated that in most patients with a lumbar disc herniation there was a significant reduction in the cross-sectional area of the psoas major on the affected side only and most prominently at the level of the disc herniation. They suggested that a correlation exists between the reduction in the cross-sectional area of the psoas major (Spearmann’s rho = 0.8; P = 0.05) and the duration of continuous sciatica of the affected side but that no correlation exists between the amount of disc herniation and reduction in psoas major cross-sectional area. Similarly, Danneels et al.29 examined the trunk muscles (paraspinal, psoas and multifidus) in chronic low back pain patients and healthy control subjects employing computerized tomography at three different lumbar levels. These authors found no significant differences in the cross-sectional area of the psoas major or paraspinals but they did find significant differences existed in the cross-sectional area of the multifidus at the L4 spinal level. Barker et al.30 investigated the cross-sectional of the psoas major in the presence of unilateral low back pain through the utilization of magnetic resonance imaging (MRI). These authors found that there were statistically significant differences in cross-sectional area of the psoas major between sides (median reduction was 12.3%) at the levels of L1–L5 and that there was a positive correlation between a decreased cross-sectional area of the psoas major and the duration of symptoms. In another MRI study, Hides et al.31 assessed the effects of prolonged bed rest on the truck muscles. This study showed that the cross-sectional area of certain muscles decreased or were unaffected by bed rest as one would imagine but surprisingly found that the psoas major and rectus abdominis actually increased in cross-sectional area. The authors attributed this increase or hypertrophy to increases in muscle tone and to the possibility that the subjects maintained a flexed truck position during bed rest, resulting in a psoas muscle shortening.