The strongest muscle, size to output, of the horse is the masseter: the muscle that moves the lower jaw. It prepares food for digestion. With its release the horse signals well-being and approval. Next in strength are the muscles of the eye balls. They account for the horse's unresting attention and quick reactions. Third is the heart. The most productive muscle involved in moving limbs is the gluteal, which spans from lumbar vertebrae, pelvis and sacrum to the thighs.
Eyes and jaw are located in the horse's stern. They connect with the core. The functions of hyoid, thyroid and larynx, nose, ears and eyes and the attachment of practically all fascia trains of the body (leave alone the long ligament) to jaw or poll explain the predominant role of head and upper neck in equitation. Limb moving muscles stretch across considerable distances. They work in teams as agonist and antagonists. Core muscles are short. They stabilize the skeleton and determine its postures. They have the unique ability to lengthen, stretch and expand of their own accord. Core muscles respond to perception. They negotiate gravity. They are at the root of limb movements. For all practical purposes the communication of horse and rider works through them. From them arises the horse's power.
The third section of the cantilevered backbone anchors the horse’s locomotive strength. From here impulsion, accomplished by three levers in pelvis and hind legs, transfers to the forehand. It is complimented by the latissimus dorsi, which - while providing an internal saddle - merges with the thoracolumbar fascia (covering the horse's upper line from thorax nine to the gluteals of the croup) and pulls the arm bone back.
The power section consists of six lumbar vertebrae. Each features an upright spinal projection and, in addition, two lateral processes, which - while resting wide and flat atop the abdomen and reproductive organs - provide for multiple muscle attachments. Also apportioned to the power section are thorax vertebrae seventeen and eighteen, which anchor the horse's diaphragm. Their role in pressure adjustment between body cavities and core functions requires further research.
Due to these twelve large lateral projections, the equine lumbar vertebra is relatively compact. No lateral lee-way is provided in the sacral joint (between lumbar area and sacrum) or in the sacroiliac joints (between sacrum and pelvis). The position of the lumbar area thus links directly to movements of the hind legs and the haunches' elasticity. In liberty the lumbar area undulates, along with abdomen and rib cage, especially in the walk. In the mounted horse, due to the closing of the croup, the three-dimensional lumbar vertebra is calm. It provides the platform from which the horse serves the rider, furnishing the base for muscle to bone attachments, both for the upper line and the lower line, as well as for abdomen, croup, arm bones and psoas.
Lumbar vertebrae. Deformations
The diaphragm is a curved muscular membrane. It separates forehand from hindquarters. The flexible middle section's upper parts (lungs and the rider's seat) thus belongs to the forehand. Liver, abdominal and reproductive organs belong to the hindquarters. The practical value of this interpretation will only come forth with further research of relating muscle trains, and the base they provide for the control of the horse's feet. Apparent is the fusion of diaphragm and the innermost transversus abdominus. It marks a transition of core musculature from front to back. Two muscle systems, the longissimus proceeding from the four lower neck vertebrae to the sacrum, and the rectus abdominus spanning pubis and sternum in the lower line, range the whole horse.
There are several cumulations of muscle to bone attachments in the power section. One focuses on rib eighteen located right below the first lumbar vertebra. Here the sternmost deep caudal dorsal serrate unites with the uppermost external abdominal oblique. From within, rib eighteen anchors the costal diaphragm. Rib eighteen thus interfaces muscle tractions in the horse's upper line and sides with respiration. Also attached to it is the internal abdominal oblique, which is responsible for the closing of the croup. The costal retractor participates. These muscles and their merger with rib eighteen will occupy us again, in respect to bending.
Another indeed impressive increase of muscle to bone attachments is found at lumbar two and three. These vertebrae provide surfaces for the longissimus and transversus abdominus. They feature the connection to the psoas major, which participates in the swinging motion of the thighs. They anchor the iliocostal, which - proceeding from the first rib - coordinates with the diaphragm in monitoring the ribs. The last attachment of the spinal muscle, participating in the horse's elevation, reaches from an anchorage between lumbar processes two and three forward to the lower neck. Muscles which abduct the hind legs and muscles which pull the arm bone back meet at lumbar vertebrae two and three. Positioned in the upper loins, in other words, these two bones provide the base for a muscular focus in equine locomotion.
The third concentration of muscle to bone attachment occurs in the hips. They anchor the above mentioned internal and external abdominal oblique as well as the costal retractor. In addition they provide surfaces for a large number of muscle groups responsible for the movement of the hind legs. Similar focal points of muscle to bone attachments exist in the horse's forehand at rib one and the elbow. The foregoing information permits the following conclusions on the hindquarter's properties and resulting challenges they present to the lumbar area.
In equine locomotion pelvis and lumbar region operate like a spring-board. As long as the sacral joint is closed and the core activated, impulsion flows through them and moves the rider's seat, shoulders, front legs, neck base and the stirring unit in the horse's upper neck up and fore (and/or back and/or side-ways). The rider sitting in his seat benefits from the haunches' ability to operate as hydraulic systems and shock absorbers alike. Haunches, lumber area and back thus unite to correspond with the features of the forehand.
New ways in old costumes
When, as seen in the sliding stop, the sacral joint opens, the spring-board turns into a break and shuts down propulsion. In principle the horse may choose any position of the sacral joint to monitor the hind legs' speed and impulsion. It not only can fully open, to the extend of leaving the horse powerless. It may as well completely close, which results in blocking flexible middle section and rider's seat, and causes the horse to buck. In the sacral joint the horse negotiates between back and haunches. It enables the change of posture, speed and direction without any interruptions in the flow of movement. This central element in the horse's biodynamics will be explored further in a later chapter.
In the horse's movements the lumbar area thus provides a solid and dependable base for all aspects of locomotion. It facilitates elevation and the way the haunches respond to gravity. Be it in liberty or under saddle. The diaphragm and functions of rib eighteen contribute. As does the concentration of muscle to bone attachments in the hips.
When, where and how much bend the horse? Preceding presentations of equine physiology suggest the following conclusion. In movement the horse's core gives laterally to the line it travels on. It undulates in accordance with the placement of its feet. In equitation the rider takes control of core and feet and ultimately limits or changes the horse's natural inclinations. He demands the continued mounting of the back. He bends the horse before his seat as the direction of movements and the subtlety of spine and ribs demand. To proceed any other way and to bend the horse in parts that are meant to be the base of strength and elevation creates complications and misunderstandings. It eliminates the option for the horse's second gear and leaves the horse demotivated.
The rider's seat and the power section
Breeding a new, faster and more powerful horse in the 1800s is at the root of the modern horse's troubles. Not only is the center of its elongated flexible middle section inclined towards warping. Its nerve impulses kick off faster. Between physical irregularities and swifter reactions the modern horse is no longer intrinsicly manageable. To do well, and be safe and sound, it requires the rider's knowledge of energy and balance. It demands time, commitment, courage, knowledge and know-how of all who deal with it. It is no longer just for fun. In addition in modern times spaces for riding have shrunk. This so much more makes the control of the horse's balance and the direction of its power an imperative for any equitation, which - beyond mere spectatorship - permits participation.
For all practical purposes the rider will do best, if at some point he introduce the horse to the half-halt. Stopping and halting for the horse is not the same. One is a shut down of power. The horse ceases to move and rests. It is supported by four legs which function as columns. The other is a control of power. The horse remains in stand-by, ready for departure. One is a downward motion, the other moves up.
There also is the distinction of halting and the so called half-halt. The former brings the horse to a stand-still as outlined above. The latter addresses the horse's activation while moving. Just what happens in the half-halt, and how to effect it, depends first and foremost on the horse's posture. For all practical purposes the half-halt works well in the elevated horse. The rider indicates upcoming changes in gait, directions and/or tasks with a renewal of elevation.
The spring-board and related features in the straight horse, bent left
