Fundamental Hip Biomechanics: Part 1

Hip Biomechanics

The following excerpted text is copywrited from the textbook; “Form and Function: The Scientific Basis of Movement and Movement Impairment” (Dr. S. Allen, Dr. E. Osar)

Frontal Plane Functional Biomechanics

The hip is a very complex joint.  It is a ball and socket joint with great stability and potentially great mobility.  One of the most critical and essential planes of motion and stability is the frontal plane of hip joint motion.  This plane (coronal/frontal) of motion and stability is largely determined by the hip abductor muscle (HAM) group through an axis of oriented in the anterior-posterior direction through the head of the femur.  The most obvious and simple function of the hip abductor muscles is to produce a movement or moment of abduction of the femur in the acetabulum in the frontal/coronal plane (as in a side lying leg lift).  As mentioned, this is a simple way to determine open kinetic chain range and open chain strength in this range but it is neither true nor transferable in theory or practicality when the foot is on the group.  When the foot engages the ground the typically usable functional range is much less and the muscular function is now to move the pelvis on the stable and somewhat static femoral head in the frontal plane.  Explained in another way, in this closed chain, the insertion of many muscles remains static and the force generated through the muscle will pull at the origin and generate movement at the joint in this manner.  In a nutshell, the hip abductor muscles (HAM) will produce either leg motion to the side (abduction) or it will produce a lateral bending or lateral flexing of the pelvis-torso into the same range of motion (abduction). 

The most critical and commonly considered hip abductor muscles (HAM) are the gluteus medius, gluteus minimus and tensor fascia lata-iliotibial band complex.  These muscles have the most favorable line of pull and all have a femur and pelvis attachment.  We will call these muscles collectively the HAM group.  In the stance phase of gait the body’s center of gravity (COG) is medial to the hip joint axis of motion.  Thus, in this single leg support phase of gait the tendency will be for the body mass above the hip to rotate or drop towards the swing leg side.  This gravitational movement should be offset by the concentric, isometric and eccentric muscular activation of the HAM group through the anterior-posterior oriented axis through the head of the femur.  Any functional strength deficits (concentric, isometric or eccentric) of the HAM group and/or neighboring synergistic stabilizers will result in an altered joint stability challenge because not only do the HAM and surrounding muscles product movement but they also generated joint compression and thus stability.  The possible undesirable outcome may be an altered movement patterning characterized by inappropriate muscle or muscle group activation in either timing, force, speed or coordination with typically coupled muscles.  These challenges to the joint and its normally expected movement patterns will result in the body’s search for more stable positions in the frontal, sagittal or oblique planes.  These newly established, yet less efficient, positions and patterns of movement are initially welcomed compensations but in time as the new accommodations become rooted in pattern the synergists and other recruitments become overburdened and further demand compensations from other neighboring muscles eventually resulting in pain, joint derangement and dysfunction.  These compensations in recruitment and movement eventually will lead to non-contractile soft tissue changes such as hip capsule pattern changes in tension and length. These non-contractile soft tissue changes can not only dictate or perpetuate the newly established aberrant joint movements but help engrain the abnormal movement patterns and their new neurologic patterns.  

Some Biomechanical Facts on Oscar Pistorius: 400 m London Olympic Games

Following Saturday’s 400m men’s preliminary heats Jere Longman’s wrote an article in the NYTimes entitled “Pistorius Advances to Semifinals”. In it were some interesting facts. Here is the link to the article. 

Ever since Pistorius’s shut out from the Beijing Olympics scientific and legal debate has continued about whether his prosthetic legs gave him an unfair advantage over sprinters using their natural legs. However, as we all knew, this time around would different in London 2012. Competing on carbon-fiber prosthetics called Cheetahs, Pistorius was going to get his chance and in the process further the debate on what is considered able and disabled.

Prior to Beijing the I.A.A.F. said Pistorius’ carbon-fiber blades violated its ban against springs or wheels that gave an athlete a competitive edge over able bodied athletes. The prosthetic legs allowed him to run as fast as elite sprinters while consuming less energy, the governing body concluded. None the less, the debate has continued over the past few years since Beijing pertaining to where to draw the line between fair play and the right to compete. In 2009 in The Journal of Applied Physiology a study concluded that Pistorius could take his strides more rapidly and with more power than a sprinter on biological legs.

An acquantance of ours who we talk to from time to time, Professor Peter Weyand at SMU Locomotor Performance Laboratory in 2009 looked at Oscar Pistorius-type carbon fiber Cheetah blades a little more closely. In his study (referenced below), in the Journal of Applied Physiology, he conducted three tests of functional similarity between an amputee sprinter and competitive male runners with intact limbs: the metabolic cost of running, sprinting endurance, and running mechanics. What he found was:

  • the mean gross metabolic cost of transport of the amputee sprint subject was only 3.8% lower than mean values for intact-limb elite distance runners and 6.7% lower than for subelite distance runners but 17% lower than for intact-limb 400-m specialists
  • the speeds that the amputee sprinter maintained for six all-out, constant-speed trials to failure were within 2.2 (SD 0.6)% of those predicted for intact-limb sprinters.
  • at sprinting speeds of 8.0, 9.0, and 10.0 m/s, the amputee subject had longer foot-ground contact times ,shorter aerial and swing times and lower stance-averaged vertical forces than intact-limb sprinters [top speeds = 10.8 vs. 10.8 (SD 0.6) m/s].

Weyand concluded that running on modern, lower-limb sprinting prostheses appears to be physiologically similar but mechanically different from running with intact limbs.

Longman’s article listed some of the other facts that have come up in recent years, facts that led to the eventual acceptance of Pistorius in London 2012’s Olympic events.  We have not captured these references specifically (yet, but we will) but in the mean time to keep this blog article timely, lets look at some of the other facts that Longman mentioned in his NYTimes article:

  • While calf muscles generate about 250 percent energy return with each strike of the track, propelling a runner forward, Pistorius’s carbon-fiber blades generate only 80 percent return, Gailey said.
  • Given that Pistorius has no feet or calves, he must generate his power with his hips, working harder than able-bodied athletes who use their ankles, calves and hips, Gailey said.
  • And because the blades are narrow and Pistorius essentially runs on his tip toes, he pops straight up out of the blocks instead of driving forward in a low, aerodynamic position for the first 30 or 35 meters, making him more susceptible to wind resistance, Gailey said.
  • Compared with runners with biological feet, Pistorius also must work harder against centrifugal force in the curves, and his arms and legs tend to begin flailing more in the homestretch, costing him valuable time, Gailey said. His stride is not longer than other runners, as many presume, Gailey said. “It’s not like he’s bouncing high with a giant spring,” Gailey said.
  • The blades “basically allow him to roll over the foot and get a little bounce,” Gailey said, adding: “The human foot operates like a spring, and his feet operate like a spring. But the human foot produces more power than the blades do.”

There is an abundance of interesting information here. We will likely return to some of these topics and facts in the future, but in the meantime we say that everyone has their own demons and deficits. We all have injuries and limitations we have to cope with, in life and in sport. So where the line gets drawn will always be a blurred. This debate on this specific case with Pistorius could go on for years and never reach an agreeable conclusion as to a fair playing field. So, let the games begin and may the best man or woman win, with his or her demons and deficits in tow.  Good work Oscar. Thanks for the inspiration.

Shawn and Ivo, The Gait Guys


We found 3 other journal articles on Pubmed on Oscar.

  1. Enhancing disabilities: transhumanism under the veil of inclusion? Van Hilvoorde I, Landeweerd L.   Disabil Rehabil. 2010;32(26):2222-7.

  2. Oscar Pistorius, enhancement and post-humans. Camporesi S. J Med Ethics. 2008 Sep;34(9):639.

  3. By designing ‘blades’ for Oscar Pistorius are prosthetists creating an unfair advantage for Pistorius and an uneven playing field? Chockalingam N, Thomas NB, Smith A, Dunning D. Prosthet Orthot Int. 2011 Dec;35(4):482-3.

  4. J Appl Physiol. 2009 Sep;107(3):903-11. Epub 2009 Jun 18.

    The fastest runner on artificial legs: different limbs, similar function?

In this PART 2 installment of Applied Hip Gait Biomechanics, Dr. Allen delves deeper into a complex topic and attempts to bring it to a level that everyone can understand and implement. Here he talks about the hip mechanics in relation to pelvic stability and gait.
It is our goal to share as much of our collective 37 years of clinical experience as we can in a medium that is usable, friendly and understandable to all viewers.
Thanks for taking time out of your busy lives to care about watching our videos.
Shawn & Ivo, ……. The Gait Guys

Gluteal Asymmetry: it means something !

Two photos above, toggle the red bar on the right.  What do you see ?

Here is a case of a young football star we saw last night.  He came in with a fresh right mid-belly quadriceps strain.  This is a simple case if you know what the visuals are telling you.  Just be sure you test your visuals (which are ASSUMPTIONS !), in other words, prove or disprove your hunches.  What you SEE is not always what is present as the problem.

You can see clearly that in a  prone position this chap has significant right gluteal underdevelopment compared to his left.  This is a “quick peak” method of screening that i do on every patient when they turn over prone on the table as he is positioned.

There are many nuiances to this case, but here is what i was thinking the moment he told me about the injury….  “Doc, we were doing short 40 sprints, and my right quad just seized up?”.

I thought, hummmm….. i wonder if he was anchoring his thigh into his glutes and abdominals.  Lets test his glutes first.  If the glute is weak then i can assume he is quadriceps dominant and not anchoring the limb into the pelvis and core correctly.  If he is gluteal inhibited, that means he will have underdeveloped glute if it has been there long enough. And if so, the glute cannot power hip extension so that range will be deficient.  Sagittal extension will occur the next level above (lumbar spine) and inhibit the lower abdominals on the right.  The hamstrings can also be called in to drive hip extension (welcome to the world of chronic hamstring issues in athletes).  And if hip extension is limited, then internal rotation is likely somewhat limited.  And if internal hip rotation and hip extension are limited then ankle dorsiflexion (“ankle rocker”) will be impaired and limited during midstance thus creating early heel rise during push off thus forcing the calf muscles to create more body mass lift than forward propulsion.

I put him on the table……saw the atrophied right gluteal……and proceeded to confirm all of the above. Treatment is based on figuring out who started this whole mess and reversing the functional pathologies in the pattern that makes sense to that patient’s neurologic system.  It can be different for each personYou cannot “cook book” good manual medicine.

Prove or disprove your differential diagnoses or hunches……. make sure your direction is the right one.  We all know what ASSUMING lead us to ……. it makes a donkey out of all of us.

We are….. The Gait Guys……. just a couple of donkeys.