The first four chapters of this book speak of a balance in the equine skeleton. The next four are about equine impulsion. In the horse's hindquarters several autonomous parts produce in perfect coordination equine locomotion. These are in addition to the hind legs the haunches, a function called the closing of the croup, the sacral joint and the diaphragm. It may be unusual to use a term borrowed from physics to speak of functions in a living body. The term lever, however, appropriately illustrates the horse's ability to produce fast forward locomotion, powerful upward impulsion and controlled movements in place.
The first of three levers in the equine hindquarters are located in the back of the horse's croup. They consist of the pelvic girdle’s two rear extensions, which - with the hind legs as their base - rotate around the hip joints whenever the horse's forehand mounts. From these muscles proceed to the sacrum above and to the knees and hocks below. An extensions at the thigh's upper end form the second levers. Muscles from here proceed to the sacrum, the pelvic girdle and the power switch. The hocks provide the third levers. In interaction with the sacrum these three levers not only produce equine movement. They accomplish what at first sight looks like a no-go. They permit the horse to lift up and move forward its relatively large and heavy forequarters with respectively light and small hindquarters.
17. Three Levers and the Haunches
The horse’s hind legs perform in cyclical repetition three distinctly different motions. They lift, move fore and down, and push off. In coordination with the front legs these are their fundamental locomotive function. But this is not all. In addition the hind legs support equine posture. Their fore and downward movement confirms the back's mounting. Their push off lowers the sacrum, in the process producing forward locomotion. Their elevation is a pre-requisite for the other phases.
In equitation a balance of the hind legs’ cyclical movement must be guarded. Their elevation, which in fact defines the quality of locomotion, is reenforced over ground bars and/or in unpredictable terrain. Their fore and downward movement, which mounts the back and calls on a weight-supporting action of the inner hind leg, is trained in classical exercises such as circles and strike-offs into canter. Their push off, which lowers the sacrum and initiates the haunches’ flexibility, is reinforced in riding forward. Jumping as a popular means of systematically training and showing horses provides a brief, rapid activation of all three phases in take-off, suspension and landing.
A word of explaination on the term haunches may be due. It refers to the hip joints, which permit a compression of pelvis and thighs, with the knees as their base. This compression is the result of a release in the illio-sacral joint. A well trained horse from the haunches initiates and fine-tunes all aspects of locomotion. They are the means of superior equine performance. Their function depends on the hip joints' flexibility, a proper balance in the hind legs' cyclical movements and an improved innervation. The latter results from the croup's closing, which I describe in the next chapter.
As regards the horse’s legs, there is another observation. The horse is made for rapid movements on planet earth. For the protection of the lower limbs it has the ability to react quickly to irregular configurations of terrain. A split-second reactionary ability, far exceeding that of man, allows the horse to not only run, jump and turn, but to travel on many different types of ground.
The before mentioned drawings 20.1 and 20.2 in John Goody, ‘The Horse’s Anatomy’ not only permitted the understanding of the mounted horse's four typical postures. They supported the foregoing analysis of how the horse’s hind legs interact with the other functions of the hindquarters. They permitted the conclusion that what I call a power switch exists in the horse's lumbar region. Each of these details forstered the understanding of equine locomotion and the rider's influence on it.
On the horse and in the research of equitation repeatedly the question came and comes up, how the rider should use his legs to activate the horse’s hind legs. Should he press his calfs towards the horse’s sides, close his thighs, close his knees or better open them. Should he touch the horse’s lower sides with his ankles or the sides of his heels, which incidently he can do only if he raises them.
And, how should his legs contact the horse. Lightly, touching it for only seconds or strongly and for the duration of several moments. How does the chose from a multitude of possible combinations? Should he attack the horse’s sides with his heels? Going as far as attacking them with spurs attached to his heels? In view of these many options I agree with the late 20th century Portugese master rider, Nuno Olivereia, who indicated that it may take some time to find out how to effectively propel a novice horse on.
Once the young horse mobilises, however, the scene changes. The touch of the rider's legs becomes lighter and the need to use legs at all less frequent. All seems to depend upon this mobilisation…
The closing of the croup is a small forward movement of the equine pelvis. It stabilizes the cantilevered backbone, mobilizes impulsion and improves the horse's self control.
Center piece of the croup's closing is the equine pelvis. This pelvis is a functional master piece. It is formed like a girdle, which from the sacral joint in the hindquarter's highest point extends sideways and proceeds towards the tail. The hip bones are the pelvis' widest lateral extension. As before mentioned it features levers. It as well provides for the passage of a foal in mares. The pelvis is fitted with several large ligament plates. Two extend from the sacrum sideways. In the illio-sacral joint the sacrum is attached to the pelvis from below.
18. The Ligaments of the Lumbar Region and the Croup
In the hip joints the horse's thighs are fastened to sockets, which are located in the pelvis girdle's lower part. The hip joints are secured by ligaments from within and without. They function as the central pivot of the horse's haunches. Between hip bones and hip joints finally stretch the cantilevered ligaments, which provide for the croup’s closing. To these the large triangularly shaped abdominal muscles are attached, which - starting at the belly's lowest point - proceed from the abdominal middle line to the loins.
19. The Hip Joint
The equine croup closes on account of the rider's weight. There may as well be a reflex, which sets off simultaniously along the eleventh rib. In this context one may want to remember the intersection of the large surcumveiling neck and back muscle right under the rider's thighs, which transfers the effect of the croup's closing into the forehand and to the neck (ill.12). The closing of the croup mounts the equine lumbar region. Correspondingly the inner hind leg steps under the eleventh rib to support the horse's weight.
20. The Ligaments of the Loins
Next to the tri-angular abdominal muscles further muscle systems support the horse’s inner organs. Balancing the long back muscle in the horse's upper line there are what one may want to call long abdominal muscles, which reach from the sternum to the hip joints (see postures).
The horse appropiates the closing of the croup under the saddle and in liberty. Only last night the opportunity presented itself to observe the closing of the croup in a group of free horses. Seeing me walk down the path along their field, they came running and - on the slope, wet gras under foot - they closed their croups in a canter's stride and went into this other, the second gear. Playing out there in the falling light each horse, according to its own intuition ran or stopped, turned or rose. As if directed by a hidden hand it was a choreography of sublime beauty.
“If only we could do this under saddle”, was my singular reaction.
Later, in the saddle, I was reminded. It is no secret and no mystery. The mounted horse learns to continuously close the croup. It becomes straight and mobilizes. With a rider's guidance it gains experience in how to handle its forces. The horse is familiar with all equine movements from playing at liberty in the fields. They need no teaching. It is the rider who stands in need. He no longer knows how to command the horse's movements. Only with knowledge and experience he discovers how to learn from the horse what it can do.
Of the functions, which make for the horse's locomotion three are discussed: the hind legs, the haunches and the closing of the croup. The sacral joint was hinted at in previous chapters. Here therefore a summary, followed by additional information.
When the croup closes the sacral joint shifts. In the process the lumber region mounts. The sacral joint is located in the croup's highest point. It consists of lumbar vertebra six and the sacrum and features a small range of motion fore and back. This motion impacts the central nervous system's sacral sections two and three. Corresponding peripheral nerves proceed from the sacral joint to the hind legs. The closing of the sacral joint improves their innervation and initiates a stand-by in the horse.
The human spinal cord is shortened to lumbar vertebra one. In the horse exists a similar however much less pronounced shortening. The shortening of the human spinal cord places all lumbar and sacral nerve sections in thorax vertebrae ten to twelve above. The equine spinal cord's shortening, being less pronounced, positions sacral nerve sections two and three into the sacral joint. Human sacral dermatomes two and three, which proceed from corresponding sections of the human central nervous system innervate the rider's seat and legs. In other words, equine performance and the rider's presence on the horse are united in corresponding nerve sections.
21. The mounted and the dropped back
As a result of the sacral joint's closure the croup's conformation changes. It gets flat (see photo). Depending on the demands at hand the sacral joint remains closed and the croup maintains it stretched position or the sacral joint returns to center position. The latter is the result of forward locomotion, which lowers the sacrum and pulls the pelvis back to normal. A sudden stop opens the sacral joint and rounds the croup. The sacral joint opens in a horse when it urinates or gives birth. It opens in a mounted horse that lacks the closing of the croup.
22. The open sacral joint
The closing of the sacral joint initiates a mounting of the lumbar area. This mounting may proceed as far forward as thorax vertebra nine, that is to the first vertebra of the equine flexible middle section. The degree of the back's mounting is balanced by the cantilevered backbone's flexibility.
The unfolding of the mounted horse's locomotion has much to do with this balance. As the equine backbone gains elasticity the horse learns to balance the degree of the sacral joint's closing and the back's mounting with the bending of the haunches and the descent of the rider's seat. It begins to fine-tune this balance according to the rider's wishes and the tasks at hand. The rider uses his bottom, legs and torso to communicate these wishes. A turn of his shoulders turns and a rotation in his flexible middle section bends the horse.
This transfer works on account of an impulse exchange between human and equine sensory-motor systems. It communicates the rider's wishes to the horse as well as informs him of the horse's current physical status. The rider, however, may call on yet another system of communication, which exists in the horse...
