The Muscular Support of the Equine Back

The musculature of the equine back is designed in a multipennate fibre pattern, for support rather than movement. The muscles fill the areas between the vertical spines of the bones of the back and the flat dorsal surface of the ribs. The muscles of the back fall into two categories, those that span short distances between neighboring vertebrae and those that extend over much of the length of the spine. The muscles of the back work together to support the spine and move the horse forward, providing suspension and propulsion. When the muscles on one side of the spine contract, the horse undergoes a degree of flexion, if the muscles on both sides of the back contract the horses back will “round”. The back muscles of the horse are continually working in a high degree of collection, ensuring constant support to the spine and ensuring the spine remains stable during any actrivity.

The longissmus dorsi is the largest and longest musles in horse’s body. It is the powerful extensor muscle of the back and also assists in lateral flexion of the spine. The gluteus medius is closely involved with the actions of the longissmus dorsi

The epaxial muscles: Iliocostal and longissimus in the back and loins, and the spinal and semispinal parts of the transverse spinal muscle convert the spine from a chain of individual bones to a rigid structure for support. Strong enough to carry the gut, and to transmit the power from the hindquarters to the thoracic limbs of the animal. The longissimus dorsi and epaxial muscles control the movement and support of the equine back, with their role being to transfer the power generated by the pelvic limbs into forward motion.

The muscles of the scapulas and pelvis support the back at either end. The nuchal and supraspinous ligaments work closely with the muscles of the back, they are of great significance to the support of the horses back; particularly when the horse is working under saddle. When these ligaments function efficiently it enables the back muscles to contribute more to propulsion rather than support.

Superficial and deep muscles involved in support of the equine back:

• Thoracic part of trapezius muscle.
• Rhomboidius thoracic muscle.
• Spinalis dorsi muscle.
• Latissimus dorsi muscle.
• Longissmus dorsi muscle.
• Medial gluteal muscle
• Deep gluteal muscle.
• Caudal part of dorsal serrate muscle.
• Lliocostalis dorsi muscle
• Retractor costae muscle
• Transverse abdominal muscle.
• External intercostal muscles.