“No abs, no back”.
To be in a healthy physical shape, the horse must be well exercised, and the training of its back muscles – and its abdominal muscles – is a key element.
Because of the anatomical limits of the horse’s skeleton, the movements of its neck and back are location-dependent. The skin, muscles, and ligaments all have an impact on back movement. However, other, less obvious factors influence the function of the back.
To better understand how the horse’s back works, it is necessary to discuss the various anatomical structures involved in the biomechanics of the horse’s back – and neck. But which anatomical structures are involved in the back movement?
The epidermis: the skin of the horse
The horse’s skin has the particularity to be very adherent to the subcutaneous tissues. This was originally an adaptation to racing and force transmission: the horse, by nature, needs to flee quickly if he encounters a predator. When a horse gallops away and engages its hindlimbs, tension is applied to the skin, which transmits the forces up to the neck area.
The multiple muscle layers
The superficial paravertebral musculature is made up of long and powerful muscles. They are in charge of large movements and are also known as gymnastics muscles. The brachiocephalic muscle, which connects the neck to the arm, for example, allows the head to move in relation to the forelimbs and vice versa. At the level of the back, the common mass, which extends from the last cervicals to the pelvis, allows forces to be transmitted from the hindquarters to the forehand.
The deep juxta-vertebral musculature corresponds to the small muscles that have kept their meta-metric aspect: they will surround – embrace – two to three successive vertebrae. Highly innervated, these small muscles are full of proprioceptive receptors. As a result, they are extremely sensitive to all variations in bearing and movement. This dense proprioceptive innervation allows for continuous vertebral readjustment. This muscular layer plays an essential role in the retention and stability of the intervertebral joints. These muscles’ work is essential because they sheath the horse’s skeleton, protect it from trauma, and keep the spine from false movements.
The superficial muscles, are composed of the ventral chain and the dorsal chain: these two chains work constantly in parallel.
The dorsal chain is composed of extensor muscles, located above the spine, running from the head to the pelvis and then behind the femur. These are the so-called paired muscles – located on the left and right side of the spine – which, when contracted, raise the horse’s head and hollow out its back.
The ventral chain is composed of flexor muscles, located below the spine. They start from the cervicals, surround the thorax (the horse has no clavicle, so the flexor muscles connect the torso to the shoulder), and then proceed to the abdominal muscles, which include the transversal and oblique muscles… which support the abdominal cavity. When this chain contracts, the horse is in flexion: the back becomes rounder, the withers rise and the hindlimbs engage under the mass. In brief, their contraction lowers the neck and raises the back.
The ligament system
The ligament system of the back, a fundamental component of the horse’s biomechanical functioning, allows the horse to lower its head – for example, to eat grass in the wild – without using its muscles when it is static – and to have a back hold. They are strained when the horse is worked head down, which causes a cohesion between the forehand and hindquarters, making the back go up. Head-down work, therefore, corresponds to flexion of the lower cervical spine or stretching of the extensor muscles.
Nuchal and supraspinous ligaments are composed of ligament strips that are inserted into the spinous processes of each cervical vertebra and are located above the spinal column. The ligament then attaches to all of the horse’s spinous processes up to the sacrum.
The spine
The spine is composed of 7 cervical vertebrae, 18 dorsal/thoracic vertebrae, 6 lumbar vertebrae, 5 sacral vertebrae and 15 to 21 coccygeal/caudal vertebrae. All the vertebrae are connected to each other via intervertebral discs, joints, ligaments and muscles.
Depending on the area of the spine, the mobility and possibilities of movement are different:
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- The cervical area is very mobile. The horse’s head can move to the left and right, as well as up and down.
- The thoracic area has limited mobility, especially at the level of the first 8 ribs attached to the sternum (D1 to D8), which does not allow for a wide range of motion.
- The thoracolumbar area is a very mobile region, thanks to the floating ribs which are much shorter. This area is sensitive in the horse, as it is often used and therefore tires more quickly.
- The lumbar area is the least mobile region in curve, due to the large transverse processes present in the lumbar vertebrae, which are very wide and flat and cannot overlap.
- The lumbosacral joint is extremely mobile and specialises in flexion-extension movement. It allows for strong hindlimb engagement under the mass and strong propulsion towards the back – but offers little latero-flexion mobility.
The digestive system
The digestive system is an element that strongly impacts the movement of the back. The intestines (colon, caecum, small intestine), which are very heavy, are suspended beneath the lumbar region of the spine. It is this single point of fixity that is the cause of colic or torsion, because, not being fixed on the sides, the visceral mass can move easily. The viscera, therefore, condition the locomotion of the horse, particularly at the trot gait.
Conclusion
The anatomy and biomechanics of the horse’s back are very interesting subjects. This area is a bridge between the hindquarters and the forequarters and allows horses to gallop at high speed, bend their necks and jump over obstacles.
A horse’s physical condition depends on its back muscles. Subject to mechanical constraints, many exercises allow for strengthening and softening the back.
SOURCES:
IFCE (2019). Fonctionnement du dos du cheval et entraînement- Isabelle Burgaud. YouTube. Available at: https://www.youtube.com/watch?v=7rhsD35vQGc [Accessed 15 Jul. 2022].
Burgaud, I. et Genoux, N. (2019) « Dos du cheval : comprendre son fonctionnement pour mieux l’entraîner » , Équipédia, 24 septembre. Disponible sur : https://equipedia.ifce.fr/equitation/disciplines-olympiques/planification-de-lentrainement/fonctionnement-du-dos-du-cheval.
Keywords: horse back, musculature, epidermis, ligament system, vertebral column, digestive system, veterinary diagnosis, equine locomotion, equine physiology, EnvA, CIRALE