| Muscles & Tendons of The Horse |
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By Stephen Champion, BSc (Hons) BVM&S MRCVS, Most movements of the horse’s body are due to contractions of its muscles. The muscles are also used to stabilise the skeleton (refer to the article in January edition of Equi-Ads) and thus prevent the horse from falling over! Muscles also generate heat by involuntary shivering and in this way maintain the body temperature - a function often required in the Scottish climate! There are three different types of muscles. Cardiac muscle forms the heart and has the amazing capacity to be able to contract and relax 45 times a minute for the entire life of the horse. For obvious reasons it never gets a break! Visceral muscle makes up a large part of the blood vessels and internal organs and is controlled by nerves and tiny amounts of hormones within the body. It is the visceral muscle, for example, which is responsible for propelling food through the horse’s intestines (or not, in the case of horses prone to impactions) and can be called involuntary muscle, because the horse does not have to think about doing this. The third type of muscle is called skeletal muscle. These are the muscles we see from the outside of the horse, and by which we can in part judge its fitness. They are mainly attached to bones by tendons and can be called voluntary muscles because they are controlled from the horse’s brain. These muscles make up about half the weight of the horse. The skeletal muscles are arranged in larger and larger units, from the cellular level up, and these parts are packed into fibres, whose combined contractions give the muscle enormous strength. Certain muscles of the horse, most notably the larger limb muscles, are provided with long, cord-like tendons. These allow the heavier muscle bellies to be placed closer to the body; since only the lighter tendons extend to the foot to operate the joints, less energy is required to swing the limb to and fro. It does however mean that long lengths of tendons are required for the horse, extending down from the knee or hock to the hoof capsule, which are prone to damage. Tendons are made from bundles of collagen, which possesses immense strength. They are quite elastic and are capable of absorbing and storing energy when stretched. The elastic recoil of these tendons makes a substantial contribution to the movement of the horse. They are prone however to serious damage due to their exposed position on the lower leg and the extreme forces applied to them by their attached muscles; this is often the case where they change direction over bony prominences. For this reason, the equines have developed through evolution highly functional sesamoid bones, which help the tendons to pull around a corner. These are found, for example, at the back of the fetlock joint, and within the hoof capsule as the navicular bone. Tendons are further protected from frictional forces by fluid-filled cushions. Is only one side of the tendon needs protection, it is covered by a bursa on that side. If a greater portion of it needs protection, a sheath may surround it. These structures lubricate the tendons as they move back and forth. Generally, tendons require a much longer period of rehabilitation than muscles when damaged. This is due in part to their relatively exposed location, away from a good blood supply. Tendon injuries are often evaluated by your veterinary surgeon using an ultrasound scanner. This will help him decide the treatment required and the prognosis for further work. Some injuries require considerable periods of box rest and if serious the horse may never return to full work. Acute and chronic inflammations of the bursae and sheaths also occur commonly and the correct diagnosis and treatment is imperative to bring the horse back into work as quickly as possible. |
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