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ESI Q and A Forums > ESI Q and A Forum > Questions and discussions for the ESI Q and A Forum > Function of the Ilio-psoas complex in horse vs. human

Function of the Ilio-psoas complex in horse vs. human
 Moderated by: DrDeb  
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Joined: Fri Mar 30th, 2007
Posts: 3295
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 Posted: Mon Sep 5th, 2011 06:53 am
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Dear readers -- this letter came in today to my private EMail. I explained to the person who sent it that I cannot engage in private correspondence with individuals by EMail, but that I would post the inquiry here in the Forum for everyone's benefit. The writer's name has been removed. As an introduction: the letter-writer's objective appears to be to find or promulgate a pseudo-scientific justification for riding horses "hollow". This has been tried before -- the most extreme example being a medical doctor who was "into" heavy-shod TWH's writing a pamphlet describing the weighted TWH "boots" as being comparable to athletic running-shoes.

* * * * * * * *

> I've been pondering the biomechanical description of Dr. Bennett's "Ring
> of
> Muscles."  I would like to offer my observations of the leverage created
> by
> the iliopsoas muscles.  I'm a physical therapist for humans.  I don't wish
> to start a compare-and-contrast of horizontal quadriped spines with the
> vertical bipedal (humans in particular) spine.  The observation is based
> on
> the pure action of the muscle between the femur and the lumbar vertebral
> bodies.  Tension across the iliopsoas will create a ventral movement of
> the
> lumbar spine and flexion of the hip joint.  Along with the ventral lumbar
> vertebral action would be a sacral nutation resulting in a more hollow
> loin
> position.  That action would not support the spine in a healthy position
> to
> carry a rider. 

Dr. Bennett has noted as a first law of muscle function:
> muscles never push.  My observation is to improve support of the pelvic
> position the antagonists to the iliopsoas must be pulling (because the
> iliopsoas cannot push the lumbar spine upward) to maintain the tensegrity
> of
> the spinal system.  My suggestion is the ring of support would include the
> gluteals and hamstrings.  In further support of my observation is the
> demonstration of parked postures having a deleterious effect by sharply
> hollowing the spine.  In a parked postion the iliopsoas is stretched and
> can
> be visualized as pulling from the femur to the lumbar while the gluteals
> and
> hamstrings are put in a slack or shortened position making them
> innefective
> for protecting a healthy spinal position.  Also, the horses that I have
> helped to improve their gaits (MFT's, I'm not a yank-n-spank trainer, but
> a
> light-handed communicator and guide) from hollow pace to collected Fox
> Trot
> required gluteal and hamstring strengthening, but only in coordination
> with
> abdominal strengthening to provide a more efficient pelvic posture.
> I look forward to a reply and hopefully a healthy discussion.

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Joined: Fri Mar 30th, 2007
Posts: 3295
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 Posted: Mon Sep 5th, 2011 07:11 am
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Dear Inquirer -- the discussion cannot be healthy when you begin it by having a vested interest. Yours, in other words, is not an inquiry which seeks open-endedly or open-heartedly from this authority the correct answer to a question, but rather is an attempt to put forward a point of view not held by me. It is also a highly incorrect and damaging point of view.

You make an old old old objection which I've heard many times before -- from certain quarters, vis., people who want to justify what is normally done to TWH's, ASB's, Morgans and Arabians to make them competitive in "park", 3-gaited, and 5-gaited show classes. Plus, the bogus or pseudo-scientific terminology that fills your letter tells me that you may be self-trained and "self-styled" as a physio, but you're not, in my estimation, likely to be a properly-trained, certified, or degreed human physio. Nonetheless, I'll do you the courtesy of making a reply -- and then let us leave it, unless you care to come to class with us in order to learn better.

The short answer is that in the human, the iliopsoas can "swing both ways", because some fibers lie far enough ventral to (anterior to) the lumbar centra, at some times and in some postures. In the human, everything depends upon what the starting configuration of the pelvis/sacrum and lumbar spine is. In other words, in humans, sometimes contraction of the iliopsoas will increase lumbar lordosis (hollow the lower back more), and sometimes it can act to coil the loins as in quadrupeds.

In quadrupeds like squirrels or dogs, that have more or less highly arched backs, the iliopsoas has only one action, and that is to coil the loins.

In horses, whose backs are not so strongly arched, the normal action is also to coil the loins. However, in badly or abnormally conformed horses, such as Arabians or American Saddlebreds that have very level resting pelvic angles, contraction of the iliopsoas can function almost as in the human -- ALMOST -- because even in the worst-conformed, worst-ridden horse, there is still no lumbar lordosis until the spine becomes absolutely pathological, i.e. "saddle backed". Then nothing works right, and that isn't what we're really talking about here.

I am aware, from correspondence sent to me many years ago by human physios who either read "Who's Built Best to Ride" (which deals with iliopsoas function in the human rider) or the horse conformation books, that they are taught a doctrine concerning the human iliopsoas which says that when it contracts, the only thing it can do is extend (i.e. "hollow") the back, increasing its lordotic curve. However, the medical literature actually says that the iliopsoas is a funny animal, which although it dictates posture can also be the slave, in some particular functions, to pre-existing posture. Go look in Grant's dissector for more about this.

As to quadrupedal animals, there is only one function, which as I said is coiling the loins. In actual fact, this is a composite movement since some of the fibers of the iliopsoas complex attach to the ventral iliac surface and some to the minor tubercle of the femur -- so that the action that results from contraction is not only to coil the loins (i.e. flex the lumbar spine and flex the lumbo-sacral joint), but also to protract the femur and cause the stifle joint to move, and rotate, laterally. These movements are crucial to equine locomotion particularly, because unless they occur the inbuilt reciprocating apparatus of the hind limb -- something the human absolutely does not have -- cannot appropriately coordinate the flexion of the joints lying below the lumbo-sacral joint.

As to the "ring of muscles" -- you mistake: this concept is not of my invention. It was first noticed by Gustav Steinbrecht's school in Germany in the 1880's, and was inspired in their minds by reading the classic "The Exterior of the Horse" by the French veterinarians Armand Gobaux and Gustave Barrier. What I did was "finish" the ring-of-muscles concept by connecting the last of the dots for horses, i.e. by figuring out how raising the base of the neck works in horses. In this work, I was inspired by the work of vertebrate paleontologist Remington Kellogg and animal physiologist E.J. Sleijper. You can read all about the history of thought on this topic in Volume I of my "Principles of Conformation Analysis."

The human physio and even the human medical doctor sometimes have difficulty visualizing function in animals because they are so used to looking at the (zoologically really very odd) human. To this end, if you're contemplating an animal side to your practice, you might like to sign up for one of my carcass dissection classes, which would give you the opportunity to examine the iliopsoas in the horse in all its glorious detail. The next class is the end of October in Bend, Oregon -- see the thread near the top of the Forum that gives details on that.

Bipedal animals right across the board get themselves into biomechanical trouble simply because they are bipeds. It's a funny thing, though, because throughout geologic time, it has been bipeds that have ruled the world. -- Dr. Deb

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