From the wisdom of Centuries to modern day's theories, flexing the horse's upper line, or vertebral column, is achieved by shortening the horse's lower line, involving abdominal muscles, pectoral muscles, and flexion of the neck.

In 1946, E. J. Slijper proposed the "bow and string" metaphor in which the horse's vertebral column is the bow that can be flexed, thereby increasing the tension of the string, which is composed of abdominal and  pectoral muscles, and those of the limbs. Later Dr Deb. Bennet focused on muscles named "scalenus" that are situated at the junction between the thoracic and cervical vertebrae. The scalenus muscles connect the string to the bow and the "bow and string" concept become the "ring of muscles."

Every principle of riding which emphasis flexion of the back through engagement of the hind legs at one end, and flexion of the neck at the other, are based on the "bow and string" or "ring of muscles" concepts.

In 1964, Richard Tucker initiated new studies of the equine vertebral column from the perspective of the forces which act upon the vertebral linkage. The polish scientist introduced the thought that the muscles attached on the vertebral bodies and their dorsal spinous processes were the superior mechanism of balance control.  These muscles are directly involved in the capacity of the horse's vertebral column to convert the thrust generated by the hind legs into forward motion (horizontal forces), and resistance to gravity and by consequent balance control (vertical forces). The pertinent evolution is that instead of resulting from overall flexion and extension of the spine, the management of the thrust generated by the hind legs is effectuated at the level of each vertebra.  "An initial thrust on the column is translated into a series of predominantly vertical and horizontal forces which diminish progressively as they pass from one vertebra to the next" (Richard Tucker, 1964) .

Five years later, in 1969, James R. Rooney (Biomechanics of Lameness in Horses), furthered the concept demonstrating that the minute rotations of each individual vertebra were coordinated through the subtle orchestration of the main back muscles that are set into mirror-image direction. More recently, in 1999, Jean Marie Denoix, (Spinal Biomechanics and Functional Anatomy) fully explained how the vertebrae rotate one around the other. The work of Professor Denoix is now regarded in the scientific world as the updated explanation of the equine vertebral column mechanism.

The work of the horse's vertebral column involves in fact two complementary mechanisms. One is the work of the abdominal and pectoral muscles complemented by the position of the neck. The other is the subtle orchestration of muscles situated above the vertebral bodies and set in mirror- image direction. Since abdominal and pectoral muscles are involved in more general flexions of the horse's vertebral column, they can be labeled as "basic" muscular mechanism. By contrast, more sophisticated adjustments are achieved by the subtle orchestration of the muscles situated directly above and below the vertebral bodies. The muscles situated directly above the middle of the vertebral bodies are referred to as "epaxial". The muscles situated directly below are referred to as "hypaxial".  Because of its ability to orchestrate the multiple and minuscule rotations of the vertebrae, this muscular system can be referred to as "superior."      

Riding and training principles focus essentially on the "basic" muscular system, engagement of the hind legs, position of the neck, etc. The science of motion regards the "basic" muscular system as necessary but elementary. Modern performances require one to educate the "superior" muscular system as well. This cannot be done with the rider's legs and hands that are acting on the "basic" system, nor through large shifts of the rider's weight that are disturbing the subtle orchestration of the muscles mobilizing the vertebrae.

All along skilled riders have "sensed" their influence on the horse's "superior" muscular system and refined, in their own way, the motion of their vertebral column. When the rider's skill was combined with particularly talented horses, great performances were achieved. Unfortunately, the rider's ingenuity  did not profit other riders because they attempted to explain their findings through the horse's "basic" muscular system.        

Gifted horses have also compensated for the short-comings in their education, by using their great talent. They are doing so however, by exploiting the strong points of their anatomy instead of better organizing their physique. As a result, they induce excessive or abnormal stresses on the limbs or vertebral column structure, thereby predisposing themselves to injuries.

The science of motion commenced with the notion that equine performances that require superior muscular coordination necessitate the ability to orchestrate the muscular system rotating the horse's vertebrae. Since the work of Leo Jeffcott in 1980, the scientific world was familiar with the thought that the biomechanical properties of the horse's vertebral column formed the basis of all body movements(Natural Rigidity of the Horse's Backbone, 1980). However, they were also aware that at this stage of evolution, the equestrian education did not have much capacity to influence these biomechanical properties. In 1998, Jose Morales wrote, "The temporal and linear stride variables reveal the efficacy of animal movement, and these are determined by the balanced movement of limbs joints.  Accurate measurements of these variables, together with knowledge of the factors which modify them, would thus be highly desirable." The factors that influence the limbs' movements are the biomechanical properties of the horse's vertebral column and these biomechanical properties can be influenced by the biomechanical properties of the rider's vertebral column.

All along, classical but visionary authors have suggested the idea. At the seventeen century, the duke of Newcastle advised total stability of the rider's pelvis. The British author divided the rider's body into three parts: two movable, from the knees down to the stirrups and from the waist up to the shoulders, and one immovable, the upper thigh and pelvis.  More recently Waldemar Seunig wrote, "The subtle S-curve of the spine allows the spine to oscillate minutely, a movement so tiny hat it is hardly perceptible to the naked eye, producing a "soft" seat. This "soft seat" differs fundamentally from a "doughy" seat, in which we find a spine that is too flexible and allowed to undulate freely in response to the horse's movement." The thoughts did not awaken much thinking because they were interpreted with the mind set on the belief that the horse's vertebral column was a swinging unit, and that gaits and performances could be improved, increasing the amplitude of the horse's vertebral column movements.

Astoundingly and in spite of all scientific measurements, such beliefs are still worshiped in modern days and even nurtured by governing bodies whose theoretical function is to ensure proper evolution of riding and training principles. The horse's vertebral column works exactly the opposite way. The amplitude of the vertebral column movements is very limited and the primary function of the back muscles is to ensure that the vertebral column movements remain within the limits of the vertebral column's possible range of movement.

One may think scientific measurements are wrong since, as a rider, one feels a large amount of motion. This was exactly my thought when I read Leo Jeffcott's study, "Thus, the total range of movement in the dorso-ventral direction of the equine back was only 53.1mm under these experimental conditions" (Natural Rigidity of the Horse's Backbone, 1980.) Fifty-three, point one millimeters is a little less than two and a quarter inches. The truth is that the rider is seated where the forces generated by the hind and front legs are having the greatest effect on the horse's vertebral column. The large amplitude of movement perceived by the rider is not the motion of the horse's vertebral column, but rather the sum of the horse body's movement. Until scientific measurements demonstrate otherwise, it was legitimate for the rider to attribute the large amplitude of movements perceived on the saddle as the motion of the horse's vertebral column.

The situation is therefore a rider's vertebral column submitted to large amplitude of movements and a horse's vertebral column limited to a minuscule range of motion. Newcastle, Seunig and many others suggested absorbing the horse's body movement while reducing the amplitude of the rider's vertebral column movements. This can be done using the whole rider's vertebral column instead of solely the lumbar vertebrae and reducing through supple tone of the back and abdominal muscles the amplitude of the rider's vertebral column movements. Harmony between the rider's back and the horse's vertebral column is not created through a    

"doughy" seat but rather a "soft" seat that is an amplitude of the rider's vertebral column movements toning the amplitude of the horse's vertebral column movements.

Furthering this concept, the science of motion discovered that the horse's intelligence, sensitivity and willingness have been shattered for centuries by excessive and confusing stimulus. Horses can learn to master the biomechanical properties of their vertebral column and in so doing, they can perform at their utmost potential and remain sound. When damages have already crippled limbs joints or other body parts, the horse has the propensity through the same vertebral column control to ease the strains induced on the limbs joints or ligaments and tendons, allowing the healing process to restore soundness. 

The late Louis Armstrong' song marvels, "what a wonderful world." When a blend of traditional and scientific thinking prepares efficiently the horse's physique for the performance, equine athletic achievements are not taxing the horse's soundness. In this case and in this case only, performing with the horse is a wonderful world.    

Jean Luc Cornille