More recently Dickx et al.32 used muscle functional magnetic resonance imaging (mfMRI) to evaluate changes in lumbar muscle activity with induced muscle pain. This study was one of the first to examine patients with acute low back pain and how it affects activity of the trunk musculature. mfMRI was obtained under three different conditions: a resting MRI was obtained after the subjects laid supine for 30 minutes; an MRI was obtained after trunk extension at 40% of one-repetition maximum without pain; and an MRI was obtained after the subjects were injected with hypertonic salt into the right longissimus muscle to induce pain and then subjects were required to again perform the back extension exercise while experiencing low back muscle pain. There were no significant changes in the psoas major muscle recruitment between resting and exercise leading the authors to conclude that the psoas major was not significantly recruited during trunk extension exercises. During the trunk extension exercises with pain induced, the authors reported that there was a statistically significant reduction in the psoas major activity bilaterally and at multiple levels whereas previous studies found it to be ipsilateral and on the symptomatic side.28,30