The psoas is a complicated muscle that has a number of critical roles in movement. I covered its anatomy, speculated and critiqued research concerning its function, and discussed assessment and training techniques in my “Secrets of the Psoas” presentation that is free to all newsletter subscribers.
Mechancially, the debate as to the psoas’s ability to rotate the femur is fierce, with some suggesting that it is an external rotator, others an internal rotator, and others arguing that it has very little rotational component. It’s equally uncertain as to the psoas’s impact on the lumbar spine during activity.
What we do know for sure is that deep fibers of the psoas originates on the anterior aspects of the transverse processes of T12 to L5 and the superficial psoas attaches to the transverse processes and intervertebral disks from T12 to L4. It courses from the superior attachments over the iliopubic eminence, across the joint capsule of the hip, to the lesser trochanter of the femur.
In the interest of today’s post, it is of particular interest that the psoas crosses the joint capsule. A shortened or hypertonic psoas can exert a significant compressive force on the joint capsule and increases intraarticular pressure. In the appropriate ranges, the ability of the psoas to contain the head of the femur is unquestionably value as Dr. Sahrmann outlines in her book. The issue lies, however, in excessive compression influencing the vascular dynamics and resulting in a number of changes.
Called the hip vascular compression theory by Dr. Warren Hammer, changes in intracapsular pressures may influence normal bone and bone marrow activities (Goddard, 1988). Additionally, intracapsular pressures may influence arthrogenic inhibition and facilitation of muscle and alter the available range of motion at the hip, particularly that of internal rotation. We all understand that joint effusions result in changes in muscular activity of peri-knee and ankle tissues (as well as distal structures) via neural reflex mechanisms. Jensen and colleagues demonstrated that at the knee, the greatest degree of arthrogenic weakness occurred with the greatest IAPs (1993). While this was not myofascial compression leading to altered IAPs, this may, potentially, be a single part of the “weak-short” psoas issue.
Dr. James Cyriax reported in his capsular patterns that at the hip, internal rotation is the first range of motion lost when dysfunctional. This pattern is evident, says Hammer, in psoas compression of the joint capsule, citing that regional anesthesia at the hip and psoas often results in alterations in reflex arc and immediate restoration of hip internal rotation range of motion. Internal rotation ROM is, of course, critical in the trigger mechanism and too much or too little can ultimately lead to a gamut of dysfunctions from sports and runners hernia to shoulder issues and many more.
Restoring proper F/A function is a critical component to making the whole system play together. As a complement to your intelligent exercise selection, those with a manual therapy license can also attempt to mitigate myofascially-reflex-induced dysfunction with some good soft tissue work on the psoas.