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This is also why backing up with the head low is so important! :)Why we should ride young horses forward and down...
It is a commonly accepted training principle that we should encourage young horses to have a low head carriage. But why is this?
The muscles of the horses back are still immature at 3,4 and even at 5 years old. This is a combination of being developmentally (age related), and physically immature, in the sense that they lack the muscle condition which comes from years of training-induced exercise. Of course the maturity of their muscles will come naturally with time, and as we work them through groundwork and under saddle. But how can we get to this point, while protecting these fundamentally weak muscles and avoiding musculoskeletal injuries further down the line?
By utilising the passive ligament mechanism, we can allow the horse to support the back and carry the weight of the rider with very little muscular effort. This allows the epaxial muscles of the back to be free to perform their primary functions in movement, rather than acting as weight lifters.
The passive ligament system of the back is primarily composed of, well ligaments, the nuchal and supraspinous ligament to be exact.
The nuchal ligament is a strong, collagenous structure, originating at the extensor process of the occiput (the back of the skull), forming attachments to the cervical vertebrae, before inserting on the spinous process of the fourth thoracic vertebrae. Here the nuchal ligament broadens in the region of the withers, before continuing as the supraspinous ligament running along the top of the spinous processes of the thoracic and lumbar vertebrae and terminating in the sacral region of the spine.
This creates an inverse relationship between the position of the head and neck and the balance between flexion and extension of the spine.
Generally speaking, lowering the head induces flexion in the thoracic region (the back is lifted) and conversely, raising the head creates extension in the thoracic region (the back hollows/drops). This is because the elongation of the strong and elastic nuchal ligament created when the head is lowered, creates a forward traction on the high spinous processes of the withers, and travels through the supraspinous ligament to lift the thoracic region of the spine. Comparatively, shortening of the ligament raises the head.
This system has provided an evolutionary advantage to the horse, as while they are grazing, the weight of the thorax and abdomen is supported passively by the ligament with very little muscular effort over long periods of time (up to the 16-19 hours per day they can spend grazing in the wild). Equally, because of the stored elastic potential energy in the liagement when it is stretched for the head to be at ground level, the horse can quickly raise its head to gallop away at the first sign of a predator.
Furthermore, lowering of the head and neck, stretching downwards and forwards, straightens out the natural S curve of the horse's spine. This lifts the bottom of the S curve, the cervico-thoracic junction and the ribcage, which creates lightness in the forequarters when the horse is moving. Further back, flexion in the thoracic region, increases the spacing between the dorsal spinous processes as the most dorsal aspect of the spine is stretched out. This posture is particularly therapeutic for horses with kissing spines.
In fact, the degree of flexion of the back is most marked between the 5th and 9th thoracic vertebrae, but is also significant between the 9th and 14th. Consequently, the arching and lifting of the back takes place directly under the saddle and therefore works to support the rider.
This is particularly useful in young horses; it allows the young horse, whose muscles are not mature enough to carry the rider, the chance to support its back and lift the weight of the rider by moving the head-neck axis rather than using active muscle contraction.
This means that the horse can use its muscles solely for movement; creating a loose, swinging back, free of tension, and suppleness in the gait.
Here we have the opportunity for us to slowly develop and condition the epaxial musculature of the young horse. Which will create a foundation of strength and suppleness of the back and the core to support more advanced movements later in their career.
Comparatively, if this system is not used, and the young horse is pulled into a shortened outline, it is the Longissimus Dorsi muscle which takes up the role of supporting the weight of the rider. But theLongissimus Dorsi is not designed for weight carrying, it is primarily a movement muscle.
Muscles act in the direction through which their fibres flow; the Longissimus Dorsi works in the horizontal plane, originating in the sacral and lumbar region of the spine and inserting through the lumbar, thoracic and ending in the cervical region. The Longissimus Dorsi primarily acts to extend and stabilise the entire spine, while also acting unilaterally to induce lateral flexion of the back. You can see the Longissimus Dorsi in action when watching a horse moving from above; the large muscle contracts alternately on each side of the back in the rhythm of the gait to stabilise the movement.
Once the Longissimus Dorsi is required to lift the weight of the rider, the muscle becomes blocked and stiff. Muscles are designed to work through a process of contraction and relaxation; held too long in contraction (to carry the weight of a rider, or support a shortened outline) and the Longissimus Dorsi will fatigue. This will lead to muscle spasm and pain within the muscle. Not only will the horse lose the strength to carry the rider, but they will also lose the natural elasticity of the back which will reduce the fluidity of their gaits.
Over time with greater overuse and fatigue, the Longissimus Dorsi muscle will atrophy, requiring the recruitment of other muscles, such as the Iliocostalis, to take up the role of stabilising the back and supporting the weight of the rider. Other muscles which are equally not designed for weight lifting. And so the cycle continues and the performance of the horse suffers.
With this knowledge in mind, we can understand why it is so essential to make use of the passive ligament system, by striving for that forward and down head carriage. Furthermore, that we also allow our young horses regular breaks, working on a loose rein to allow our horse to come out of the outline, stretch out, and reduce the risk of fatigue.
I always marvel at the intricately designed systems of energy conservation to create efficiency in the horse's way of going. It is our role as a rider to have an awareness of and make use of these systems; to allow our horses to go in the most efficient and beneficial way for them possible, upholding their standard of welfare.
Image credit: Tug of War, Gerd Heuschmann ...