Conference noted::equitation

1882.0. "Can horses bend their bodies?" by DECWET::JDADDAMIO (Seattle Rain Festival: 1/1-12/31) Wed Apr 27 1994 19:43

Can horses bend their spine around the rider's leg or not?
    
    That was recently debated on usenet. I remembered reading an article
    several years ago and looked it up.
    
Here's the answer from Dr. Hilary M. Clayton, a veterinarian and PhD
who is a professor of veterinary anatomy. The following exceprts from
her 1987 article "Structure and Movements of the Normal Equine Spine"
published in Equine SportsMedicine should answer that question. Any
comments enclosed in [] are mine. BTW, don't worry she defines most of
the terms she uses. It's pretty easy to understand because that journal
was aimed at a combined audience.

"REGIONS OF THE VERTEBRAL COLUMN
...
The main part of the back, from the base of the neck to the pelvis,
comprises the thoracic and lumbar vertebrae. The thoracic region,
extending from the withers to an area just behind the saddle, usually
consists of 18 vertebrae, known as T1 to T18. Sometimes there are 19, or
occassionally 17, vertebrae in this region. The withers are formed by
the elongated spinous processes of the first few thoracic vertebrae.
Individual variations in the length of these processes determine how
prominent a horses withers are. ...

MOVEMENTS OF THE VERTEBRAL COLUMN

The total flexibility of the vertebral column is the summation of the
small amounts of motion at each joint complex. Three basic types of
movement occur. ... Flexion and extension are the movements that
arch(or round) and dip(or hollow) the back and neck; lateral bending is
movement to the left and right sides; and rotation is twisting around
the central axis of the vertebral column. The amount of each type of
movement at a specific intervertebral joint depends on the shape of the
bones and the restrictive effects of the surrounding ligaments. Recent
research studies have described precisely the amount of movement in the
three directions at each joint from the base of the skull to the plevis.
The results of these studies, which are illustrated graphically in
Figure 4, will be described in relation to the functions of the back and
neck."

[Here Dr Clayton inserts 3 graphs: Graph 1 show betweens 20 and 80 degrees
flexion and extension for the vertebrae of the neck and *at most* 5 
degrees for the thoracic vertebrae. Graph 2 shows between 20 and 40
degrees of lateral bending for all joints of the neck except that
between the first and second neck vertebrae. Graph 2 also shows about 10
degrees of lateral bending for the thoracic joints T10 through T15. Note
that this is twice as much as these same joints of the back can
round/hollow! The rest of the back shows slightly less ability to bend
sideways. Graph 3 shows the horses spine can rotate very little
except at the joints between the head/neck and the first 2 neck
vertebrae. For the rest of the vertebral column, the area under the 
saddle shows the most ability to rotate and that is about 5 degrees. Now
back to Dr Clayton's own words...]

"Lateral bending of the horse's back is greatest at the level of T11 to
T12, i.e. the area under the saddle. For many years the horse's ability
to bend around the rider's inside leg was a controversial topic but, as
a result of new research findings, we now know that the back as a whole
has some lateral mobility. This [ability to bend the back] is augmented
by the ability of the shoulder blades to slide back and forth on the
chest wall, since the horse has no clavicle[collar bone] to restrict
shoulder movements. Lateral bending is maximized through the use of
schooling movements(turns, circles, lateral work) to enhance
flexibility.

Lateral bending of the thoracolumbar spine is always accompanied by
axial rotation, with the spinous processes rotating towards the convex
side of the curvature."

Hope that helps,
John

    The pragmatic answer of experience is that a horses will not bend its 
    body on command from its rider. It will only its body when it needs to
    scratch an itch on its rear leg with its teeth. This is most likely to
    happen after aforesaid rider has just dismounted after spending 60
    fruitless minutes trying to get the horse to bend.  

    Monsieur,
    
    The question was "Can they bend", not "Will they bend?" ;-) The answer
    to the former is "Yes" while the answer to the later is sometimes "Not
    a chance!"
    
    Seriously, I think you bring up one of the reasons that the debate even
    arose. Many years ago(but sometime in this century), some moderatley
    well known equitation author(I think it was Littauer) put tape done the
    middle of a horses back and led the horse in a small circle. He(whoever
    it was) then published photographs showing that the tape was still
    straight while the horse was on the circle. He claimed that this
    "proved" that the horse couldn't bend it's spine laterally. You may
    have seen something similar to this in EQUUS a few years ago because
    they repeated his experiment.
    
    I always believed that this experiment proved only that the horse in
    the photos *chose* not to bend because it was easier to swing its 
    haunches out. In fact, the photos EQUUS printed *clearly* show a
    horse with its haunches out.
    
    Anyway, I was glad to find scientific evidence such as Dr Clayton's to
    support my own opinion(which is that horses can bend but are reluctant
    to do so if their is an easier option).
    
    Another interesting point that Dr Clayton's article brings up is that
    horses have *extremely* limitied ability to round their backs. It is
    substantially less than their ability to flex sideways. Yet, no one
    has ever questioned whether or not horses can raise their backs! Why?
    Because it's easily seen/felt and there are no other choices to explain 
    what we see and feel.
    
    John