EXERTION AND ITS EFFECT ON THE HORSE. We ask our horses to exert themselves whenever we work or compete them, whatever the discipline. Whether we gallop a racehorse to get it fit to run, school a dressage horse, or simply hack out quietly. Some exert themselves more than others but they are all large animals which must exert effort in order to propel their bodies forward. Even at slow paces we ask for self carriage, an outline, straightness and controlled movement so even if there is not a great deal of aerobic exertion the muscles, tendons, ligaments and joints are still working hard. Once aerobic effort is required ie galloping and/or jumping the respiratory system must also be ‘fit’ to send oxygen around the body as quickly as possible to keep the muscles working efficiently. The blood also takes away lactic acid from the muscles and it is when there is lactic acid build up and a reduced intake of oxygen that the body has to slow down. It is also more likely that a muscle will fail at this stage then any other and so a joint such as the knee or fetlock may over-extend resulting in tendon or ligament damage or even fracture. So fitness to do the job required is a vital part of injury prevention. Weeks of slowly building up fitness and workload are necessary to attain the level of fitness needed for the job in mind. Even with perfect conformation the performance horse and its joints are subjected to daily wear and tear. The joints are designed to absorb shock, permit frictionless movement, and bear the weight of the body. 60 – 65% of the weight of the horse’s body is borne by the forelimbs and they are thus subjected to greater concussive effects than the hind legs when the horse is moving at speed. The concussive force on the front legs is much increased when the horse gallops, leaps over a large fence and lands on its front feet especially onto hard ground. Some injuries are more common place in horses doing a particular job. Young thoroughbreds in training are prone to chip fractures of the carpal and fetlock joints from galloping at speed on hard ground. When fatigue sets in the joints can become over extended with backward deviation of the carpus and extreme dropping of the fetlock. In this position there is a possibility of chip fracture. Epiphyseal injuries can occur because the growth plate is weaker than the surrounding bone and ligaments of the joint capsule. What may produce a torn ligament in an adult animal may produce a traumatic separation of the growth plate in a growing bone. In dressage, especially at advanced levels, the horse is required to move his centre of gravity backwards, putting more stress on the hind limbs. Some lateral movements can cause high joint stress particularly of the hock. Horses which load more weight on the rear are more prone to hock, rear fetlock and stifle injuries and disease. In a jumping horse there is great stress on the hind limbs on take off and on the entire front limb suspensory apparatus on landing. Additionally, it is often asked to turn sharply after a jump in order to line up for the next, placing severe stress on the hocks. Lameness may occur as a result of a single trauma to a joint or repeated traumatic episodes. When joints suffer trauma the articular cartilage inside the joint is damaged and is unable to repair itself. The result is traumatic arthritis which may be inflammation of the joint lining (synovitis), inflammation of the joint capsule (capsulitis), injury to supporting ligaments of the joint (sprain), or fractures to the bones within the joint. The repeated shock of impact with the ground is responsible for the development of osteoarthritis (Degenerative Joint Disease). In DJD the onset of lameness is gradual. As the hoof strikes the ground a shock wave travels up the limb. Initially changes to stride length are imperceptible but the horse is changing his way of going to avoid the pain in a joint caused by a particular movement. Muscles tighten to protect the limb but as the disease progresses the joint is susceptible to more concussion and the muscles of the back start to take on a protective role resulting in the whole body appearing stiff and restricting free movement. The neck, chest and shoulders are of paramount importance to the action of the forelimbs. The main nerves which feed the forelimbs leave the spinal cord between vertebrae in the lower neck (C6 –T2). If a horse struggles to flex and bend its neck to each side, up and down, shows stiffness or pain reactions it will cause restricted limb action, reduced ability to gallop, reduced speed and reduced stamina. The main nerves which feed to the hind limbs leave the spine in the lumbar and sacral region (L4 - S2) and inflammation, soreness and pain in this area can and does cause the horse to take a shorter hind stride or unequal hind strides. The result of this will be a reduction in power leading to slower galloping speed and/or reduced stamina and failing to stay the distance. The inexplicable poor performance of any horse could be attributed to any of the above. By being vigilant to the signs of over-exertion and by allowing for recovery of the musculoskeletal system after work these problems can be minimised. The signs can be subtle but they are there – sometimes rest is needed, sometimes an injury has occurred which will require treatment. By palpating the spine, limbs and muscles the manipulation therapist gains information about sites of pain throughout the body. By correcting subluxations and misalignments the manipulation therapist is removing sites of pain, relieving stresses on the nervous system and restoring balance and straightness to the whole body. Maintenance examination and adjustment should be part of the routine care of the equine athlete as this will maintain full function of the musculo-skeletal and nervous systems before any permanent or long term problems occur. .