HIP ASSESSMENT SERIES PART 13: THOMAS TEST FOR ILIOPSOAS TIGHTNESS Hip flexion can be impaired not only to a tight rectus femoris muscle but more often than not due to tightness of the iliopsoas muscle. The Thomas test is the most common quick test to assess for contractures or tightness of this muscle that runs from the lateral part of the segments T12-L4 and the iliac fossa to the lesser trochanter. | Physiotutors