Changes in psoas muscle T2 for the side with a higher T2 at baseline (A) and the side with a lower T2 at baseline (B) in subjects with acute low back pain following a single osteopathic manipulative treatment (OMT) session. Data are plotted for individual subjects (open symbols) along with the mean response (filled square symbols). Data were obtained before manipulation (baseline), immediately following OMT and 48-hours following OMT. We observed a significant change in psoas T2 asymmetry following OMT. Follow-up analysis indicated that the side with the higher initial T2 value did not change immediately following OMT despite exhibiting a modest effect size (+eta2 = 0.51), but that it was reduced 48-hours after OMT (*p = 0.04, eta2 = 0.61). The side with the lower initial T2 value increased immediately following OMT (*p = 0.04, eta2 = 0.61), and returned back to baseline levels after 48-hours.