Measurement of Psoas Major Correlating with Functional Performance in Asymptomatic Adults—An MRI and Ultrasound Study

ABSTRACT Introduction/Purpose Contraction of the psoas major (PM) stabilizes the lumbar–pelvic–hip region. Most studies use invasive radiology and expensive tools to determine the muscle width (MW) and cross-sectional area (CSA) or to activate the PM. Few studies use dynamic ultrasound imaging (USI). This study establishes the reliability and validity of dynamic USI for the measurement of MW and CSA of the PM, compares the results of three different lumbar–pelvic–hip stabilization tasks for resting and contraction, and determines the correlation with functional performance. Methods The muscle CSA (CSA MRI ) and width (MW MRI ) of the PM at the level of the third lumbar vertebra were measured in 19 asymptomatic adults using magnetic resonance imaging (MRI). USI was used for three tasks: pull-knee-approximate-hip, short lordosis, and active straight leg raise. The CSA (CSA USI ) and width (MW USI ) of the PM on the right side of body were measured using USI. On the same day, Timed Up and Go and five-repetition sit-to-stand (5R-STS) tests were used to determine functional performance. Results Reliability values for the MW USI and CSA USI were excellent for the three tasks. MW USI and CSA USI were significantly correlated with MW MRI and CSA MRI ( r = 0.71–0.99). All tasks significantly increased the MW USI and CSA USI for PM contraction. In terms of the relationship between functional performance and changes in MW USI or CSA USI (ΔCSA USI ), only ΔCSA USI was negatively correlated with the results for 5R-STS ( r = −0.49, P < 0.05). Conclusion USI is a highly reliable method to measure the PM. The tasks for this study activated PM contraction, but there was no significant difference in contraction for the tasks. Measuring PM using USI gives real-time dynamic information during muscle contraction with functional performance.