From the Vault: ‘STOP BLAMING PSOAS’
Picture courtesy of Primal Pictures
I have heard many times in casual conversation and case demonstrations at various soft tissue seminars when observing/discussing running gait, “if the hip externally rotates during the swing phase that means that the athlete has an overactive psoas.” The idea here (better described as a myth) is that because the psoas muscle makes its distal insertion into lesser trochanter of the femur, it acts to externally rotate the hip as well as to flex it. Thus at the end of stance phase of the trailing leg, during the first half of the swing, and over active psoas will cause external rotation of the hip in addition to its action of producing hip flexion.
WAY back in 1999, Skyrme et. al, in the journal ‘Clinical Anatomy’ (12:264-264, 1999) demonstrated that this is in fact not the case:
“The psoas and iliacus muscles, along with their common insertion, were isolated by dissection in six adult cadaveric specimens. The action of psoas muscle was assessed by pulling the muscle along its long axis and then observing the effects on rotation of the femur, with a visual estimation of the rotation in degrees. Conclusion: Traction applied along the long axis of the muscle produced hip flexion with NO rotational component.”
To further debunk some common myths Yoshio, et al., in 2002 (Orthop Sci, 2002;7:199-207) concluded that the primary role of the psoas major was for lumbar stability and that the psoas major contributed VERY LITTLE to hip flexion. He explained that the primary role for the psoas major is at the hip for stability. This was achieved through maintaining the femoral head in the acetabulum.
Well then psoas must act to flex the lumbar spine….right? Based on his studies Bogduk (Clin Biomech, 1992;7:109-19) does not believe the attachment of the psoas muscle has a long enough lever to act as a prime flexor of the lumbar spine. His studies indicate that in erect posture, the psoas exerts an extensor moment on the upper lumbar spine and a flexor moment on the lower segments. The major forces acting on the lumbar spine are compression and anterior shear forces. The psoas has a primary stability role at the lumbar spine for axial compression and it has a minimal movement function on the lumbar spine.
To quote one of my articles in Canadian Chiropractor “Medical research can only be considered effective if it changes the practices and/or mentality of its intended audience in a way that, ultimately, benefits patient care.”
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I liked the fact that this article made me think, but the complexity of the thought hurt my brain. Flexion of the Lumbar spine must come atleast some what from the Psoas Muscle, or is it only Gravity. I thought of my 300 lbs cadaver in the anatomy lab, Rectus abd is not present and to move that L/S while looking at the Psoas Muscle, which was huge, it only made sense. I work with the Rowing Team in Italy and I blame losts of problems on the over active Psoas. What would you propose to be a stretch if if the psoas is not acting as a Lumbar flexor? ART and Graston go ant and through the abdominale cavity as you know. I really appreciate your articles and the great information, so dont take this statement as an attach. I just love to learn and make sense out of it to use in my practice and in helping all patients. Thanks