The core in a horse is just as important as it is in humans. Yet, relative to the emphasis most gym goers place on these muscle groups, most horse owners spend comparatively little time focusing on the horse’s core. Unfortunately, this often leads to our horses moving incorrectly and using unhealthy movement patterns to compensate for the weakness in these ‘core’ areas.
Interestingly, in the horse, the core is not just made up of the ‘abdominal’ muscles, as many of us seem to think; the core is made up of all the structures that provide support to the horse’s frame, from the poll right down to the end of the tail. In this article, you will see that the neck, trunk, pelvis and thoracic sling muscles are all crucial structures that must be targeted through core training.
Bony structures
The horse’s core is built around the vertebral column, consisting of seven cervical vertebrae, 18 thoracic vertebrae, six lumbar vertebrae, five sacral vertebrae and about 20 caudal vertebrae that make up the tail. In the thoracic region, the ribs and sternum are also considered part of the structures that make up the bony part of the core, and these structures move with the vertebral column. Similarly, the pelvis (with its associated hip joints), which is attached to the sacrum at the sacroiliac joint, is another bony structure of the core.
Core movements
Three types of movement are possible in the spinal column. The first is rounding and hollowing (flexion and extension), the second is side-to-side (lateral) bending, and the third is twisting (axial rotation). The amount and type of movement differ in each particular section of the spine, with the cervical spine (the part in the neck) having the most mobility.
The ridden horse must learn to use his muscles to provide appropriate degrees of mobility and stability in the joints of the neck, back and pelvis. Specifically, the pelvis, hips and spine must be sufficiently stable to allow the transmission of propulsive forces from the powerful muscles of the hindlimbs through the rest of the body. All of this means that the muscles involved in supporting these key bony structures are vital for the health and performance of the horse. These core muscles are discussed in some detail here.
Core muscles
The abdominal, sublumbar and epaxial muscles move and stabilise the vertebral column, so these muscles are considered integral to the core. The front legs, which lack a clavicle or bony shoulder girdle to support them, are attached to the vertebrae, sternum and ribs by the powerful thoracic sling muscles. These muscles adjust the position of the sternum, ribcage and withers when the forelimbs are on the ground, and they are therefore also considered a part of the core. The pelvis is then attached to the sacrum at the sacroiliac joint, and the pelvis and hips are stabilised through the work of the pelvic stabiliser muscles. These muscles are thus also included in the core group. Finally, the neck has a huge influence on the movement and weight distribution of the horse, so the neck muscles are also included as part of the core musculature.
Abdominal muscles
Includes: rectus abdominus, transversus abdominus, and the internal and external oblique muscles.
The abdominal muscles round the back by flexing the intervertebral joints (the joints between the individual vertebrae) and bend the spine laterally (from side to side). Contractions of these muscles are visible in front of the horse’s flanks.
Sublumbar muscles
Includes: iliopsoas and psoas minor.
The sublumbar muscles run from the underside of the thoracic and lumbar vertebrae to the front of the pelvis and femur (thigh bone). These muscles work with the abdominal muscles to round the thoracic, lumbar and lumbosacral joints of the spine. These muscles also assist in flexing the hip and stabilising the spine and the pelvis.
Epaxial muscles
Includes: multifidus, longissimus and iliocostalis.
The epaxial muscles lie above the vertebrae’s transverse processes (the sideways protrusions). The deepest layer of muscle is made up of multifidus, which lies next to the vertebral spines (the upward protrusions). This muscle has short fibres that stabilise and align the vertebrae so that propulsive forces from the hindquarters can be transmitted forward without dissipating.
The more superficial muscles (longissimus and iliocostalis) are long back muscles that control the amount of rounding of the spine and cause lateral bending. These muscles can also increase the effect of gravity in hollowing the back.
A note on back pain and the epaxial muscles
When a horse has back pain, the epaxial muscles may be held in contraction, inhibiting the back’s rhythmic undulations in an attempt to reduce pain. Atrophy of multifidus often occurs with back pain, which interferes with the horse’s ability to stabilise the spine for any collection. When back pain resolves, multifidus may not regenerate unless stimulated through specific core training exercises. The other epaxial muscles regenerate more readily than multifidus.
Under optimal conditions, the epaxial abdominal and sublumbar muscles contract and relax in a coordinated manner to round, bend and stabilise the back. These movements are necessary for any collected work. Due to their function in aligning and stabilising the thoracic and lumbar regions, the development of adequate strength and correct functioning of these muscle groups are key in preventing and rehabilitating back pain.
Thoracic sling muscles
Includes: serratus ventralis, pectoral muscles and subclavius.
The thoracic sling muscles attach the forelimb to the trunk. Tension in the left and right sling muscles affects the position of the withers and ribcage in relation to the front legs. When the front legs are on the ground, the action of both sides of the thoracic sling muscles raises the sternum and withers and assists in rocking the horse’s weight back onto the haunches. One-sided action of the thoracic sling muscles affects the straightness and position of the shoulders.
Pelvis stabiliser muscles
Includes: sublumbar muscles, middle and superficial gluteal muscles, tensor fasciae latae, biceps femoris, adductor, sartorius and sacrocaudalis dorsalis.
These muscles stabilise the pelvis and hip joints, which link the hindlimb and other core structures. Instability in this region allows propulsive forces from the hindquarters to be lost through inefficient transmission and also interferes with balance.
Neck muscles
Includes: splenius, semispinalis, braciocephalicus, sternocephalicus, omotransversarius, serratus ventralis cervicis and the deep stabilising muscles.
The neck is intrinsically much more mobile than the other spinal regions. Neck movements affect the horse’s balance and weight distribution and also influence the movement of the rest of the spinal column. The muscles on the top of the neck, including splenius and the underlying semispinalis, act to either extend the neck or to support the neck from above. Serratus ventralis cervicis raises the base of the neck.
Contraction of the muscles on the underside of the neck (braciocephalicus, sternocephalicus, omotransversarius) creates undesirable tension and an ‘inverted outline’ with a thickened under-neck. This is unfortunately commonly seen in many dressage horses today and is evidence of incorrect training and riding. The deep stabilising muscles of the neck, including the cervical multifidus, stabilise and move the vertebrae.
Take home message
While these Latin names can feel overwhelming, what is important to understand is that the core does not just consist of the abdominal muscles but instead the muscles supporting the entire spinal column of the horse. Without specific work, these muscles cannot perform their roles adequately, and this lack of stability and strength predisposes our horses to injuries through incorrect or compensatory movement patterns. In our next article, we look at ways to strengthen these key areas and build them up so that our horses can perform at their best for as long as possible.