Next up is a great piece from some of the brightest minds in human movement and therapeutic intervention via exercise. Today’s summary is of:
Lewis, Sahrmann, and Moran. “Anterior Hip Joint Force Increases with Hip Extension, Decreased Gluteal Force, or Decreased Iliopsoas Force.” Journal of Biomechanics 40.16 (2007): 3725-731. Print.
It is known that abnormal loading of the hip capsule can lead to subtle instability or anterior hip pain, and this loading has the potential to lead to acetabular labrum tears. It is theorized that reduced function of the gluteus musculature and the iliopsoas muscles can contribute to anterior glide of the femoral head during extension or flexion, respectively. As distance runners spend a great deal of time executing both movements without necessarily taking the time to cross train, they may be at a particularly high risk of anterior hip pain as it relates to anterior glide.
The authors sought to identify that weakness can contribute to increased anterior joint forces and increased anterior hip pain, instability, and labral tearing.
Materials and Methods
The authors utilized a three dimensional computer model of the pelvis, thigh, shank, and foot all on the right side with 6 degrees of freedom based on the major movements attainable with each joint structure. The moment arms of respective musculature was determined based off of known research.
It was determined that increased anterior forces would equate to femur contact with the acetabulum with no regard for the position of the femur.
Once modeled, the authors placed the hip through two exercises–prone hip extension and supine hip flexion with a control, 50%, 25%, and 5% of normative strength values.
It was demonstrated that decreased gluteal function by 95% of normal led to 156N greater forces on the anterior hip, which equaled 19.2% of bodyweight. It was also shown that when gluteal strength was reduced, the involvement of the semimembranoses became the major contributor to joint forces. With greater hip extension, joint forces rose.
Additionally, as psoas was reduced to 5% of normal joint forces rose by 112.4N, equaling 14.1% of bodyweight, leading to more forces from the adductor longus.
It appeared that three conditions led to greater anterior joint forces; decreased function of the gluteals in extension, iliopsoas in flexion, and greater hip extension angle.
According to Sahrmann, her clinical experience has shown that those with anterior hip pain present with minimal gluteal function and psoas function as well as facilitated TFL and sartorius.
It was theorized that the increased contribution of semimembranoses to anterior joint forces was due to its reduced external rotation moment arm and ability to adduct, which allowed the sartorius and the TFL to contribute to maintaining a degree of medial rotation, that keeps the femoral head out of the danger position of external rotation that is correlated with labral tears.
The authors contend that 14-20% increases are significant despite the joint routinely handling 4 or more times body weight during gait for a number of reasons. First, the increase was only anteriorly measured, not total. Secondly, they note that the acetabulum has minimal bony containment and relies strongly on soft tissue restraints that can be damaged with lower forces (especially in repetitive motion).
It is also theorized that those with anterior hip pain can decrease pain by improving motor control of said musculature. Additionally, the psoas tendon may play a role in buttressing the anterior joint capsule during extension, so it may be important in both flexion and extension related anterior joint forces.
Using this in practice
We all know (or should know) that training the gluteals can lead to powerful effects locally and at distal segments of the body, and it has been much ballyhooed in performance literature. The iliopsoas (a name with which I disagree) is one that has been noted, but not from a control of the femoral head standpoint.
Training hip flexion may help to reduce anterior capsule forces as well as contribute to stabilization of the lumbar spine (though McGill disagrees). My favorite first step is a supine flexion isometric above 90 degrees as it reduces gravity’s pull and isolates the psoas well. From there, I’ll progress to a more gravity loaded exercise that begins over 90 degrees of flexion before moving to full range of motion exercises.
The simple addition of exercise interventions can help reduce runner’s anterior hip pain syndromes and prevent acetabular labral tearing, a common injury. Again, these should not be “focus” exercises, and should/can be used as part of a warm up or as “fillers.”