There is more to the shoulder than meets the eye. Firstly, it is important to realize that the horse’s shoulder is not actually attached to the spine by a collar bone as it is in humans. Instead, the shoulder is attached to and supports the weight of the front end by sheets of muscle. These sheets of muscle attach the shoulder blade from various points along the cervical vertebrae (bones of the neck), the thoracic spine, and to the ribs. Because of this, the shoulder is designed to be a shock-absorber. It is this design that allows the horse to travel at speed without excessive jarring on the skeletal system (and in turn, the rider).
The angle of the shoulder blade also largely influences the absorption of concussion. Ideally, the shoulder should be long from the point of the shoulder towards the withers. It can be identified as the flat bone structure that suspends anywhere from 2 to 6 inches below the withers and slopes forward gradually developing more muscle coverage. As opposed to a shorter, more upright shoulder, a long sloping one allows a greater stride length as well as more opportunity for muscle to attach the scapula to the skeleton of the horse. With more room for muscle, there is a greater potential for stronger movement, better carriage and increased athletic ability. A shorter, upright scapula is not designed as efficiently to absorb the concussion of the front legs when the horse is traveling, has less space for muscle attachment, and a more limited range of motion.
The shoulder depth is measured from the chest, where the base of the neck attaches, to a line drawn down from the withers, and from the withers to the base of the thoracic cavity (the bottom of the ribs), much like a misshapen box. More space in this area also means more space for the scapula to move without limits set by other bony anatomy. If there is a greater depth in this area, there is more freedom of movement contributing to greater expression and a longer stride.
In most horses, the angle of the scapula is an angle parallel to the pastern of the forelimb. Ideally, this angle is 45 degrees, allowing for optimum shock absorption without being in lack of support or lack of flexibility.
Function in Movement
As mentioned, the muscles attaching the shoulder are responsible for absorbing the concussion of the horse as it travels. When the foreleg is in standing position, this is, generally, the halfway point in mobility. As the horse travels forward, the middle and base of the scapula is pulled forward by muscles in the neck, bringing the foreleg forward, and thus, slopes the upper part of the scapula slightly backwards as it is pulled by muscles behind the withers. As that leg becomes weight bearing in movement, the muscles along the back of the scapula that attach it to the ribs and thoracic spine pull the middle and base of the scapula backwards. These muscles, therefore, play a large part in creating good movement. The importance of good shoulder movement is paramount, especially for disciplines such as dressage, jumping and racing.
In racing, the more efficiently a horse can cover a longer distance means a better racehorse. Part of this efficiency is determined by the range of the shoulder blade. If the scapula is long and sloping in a deeper shoulder area, more ground can be covered per stride which means less strides required to cover the same distance, and thus less energy lost.
For jumping, the more reach a horse has determined by the slope and space provided for the scapula not only increases his athleticism between jumps, but actually provides more flexibility for tucking his legs up when he jumps over the obstacles. Jumping, like racing, demonstrates the necessity of good shock-absorption in the shoulder.
As for dressage, the liberty of the shoulder is vital for correct movement and for performing the individual movements correctly. A freely moving shoulder is required to be successful and to create more reach in an uphill stride.
Because the shoulder is attached by muscles alone, even a mature horse has the potential to get taller. It sounds impossible, but in actual fact, when the muscles that attach the scapula to the spine and ribs are exercised appropriately, carrying the horse in an uphill stride, these supporting muscles get stronger so that even when the horse is at rest, the muscles are naturally holding the front end of the horse’s body a little bit higher off the ground.
Since the role of the shoulder is vital for better movement and athletic ability, it is of utmost importance for riders to have saddles that allow free movement of the shoulder blade. Saddles that pinch the withers restrict the scapula as it slopes backwards when the foreleg is raised and will actually decrease overall stride length. It is also important for riders to allow the neck to stretch naturally (as opposed to trying to hold the horse in an artificial frame), so that the muscles of the neck that pull the scapula forward can do their job properly and not be limited to those muscles that act on the foreleg alone. By allowing and encouraging freedom in the shoulder, the horse will have a better stride and develop the muscle that makes him more athletic and that much more beautiful.