The hip flexors are a group of muscles that act to flex the femur at the hip joint. The primary movers are the rectus femoris and iliopsoas. The pectineus, sartorious and hip adductors also assist in the action of hip flexion. An easy way to visualize this action is bringing the knee towards the chest. The hip flexors are often blamed when dysfunction is present, but it is important to know how to truly assess for hip flexor tightness.
The Thomas test is a simple tool to help determine if your hip flexors are tight. The individual will lie down on the table on their back. The individual will then bring one knee towards the chest while the opposite leg stays on the table. If the bottom leg rises off the table as the hip is flexed then it is a sign for tight hip flexors on that side. Another variation of the test would have the knee hanging over the table. If the bottom knee goes into extension as the opposite knee comes towards the chest, then it indicates a shortened (tight) rectus femoris.
Be sure to watch the video for a brief demonstration. Some common mistakes are allowing the pelvis and low back to come off the table, as well as allowing the pelvis to tip. This will compensate for the hip flexors and allow the test to appear normal. Another trick is to have someone palpate under the quadratus lumborum/ superior spine of the hip to make sure that the low back and pelvis are not compensating.
Alex Edwards, CEP, CSCS
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Vigotsky, A. D., Lehman, G. J., Beardsley, C., Contreras, B., Chung, B., & Feser, E. H. (2016). The modified Thomas test is not a valid measure of hip extension unless pelvic tilt is controlled. Peerj, 4e2325. doi:10.7717/peerj.2325