Movement is what horses are all about. In fact, they evolved from the fox terrier- sized Eohippus of 55 million years ago mostly because of their ability to move. Movement is still essential to every horse’s nature and even his life. A horse that cannot move is a horse in trouble.
The Anatomy of Good Movement
In order to understand the basics of good movement, it helps to know a bit about the horse’s anatomy. All horses –Thoroughbreds, draft horses, ponies, or even zebras – have the same anatomy and locomotion, although their conformation and action are quite different.
The skeleton is the horse’s framework. The bones support him and act as levers to move the body. The skeletal muscles move the bones; various muscle groups each have their role to play, and the entire muscular system works together in a coordinated effort, in a “circle of muscles” around the body. In good movement, muscle groups work in harmony and balance, and no single muscle or group is overstressed or left out of the picture. Poor movement overstresses some muscle groups and underutilizes others, resulting in incorrect muscle development, such as a neck that bulges on the underside, lack of muscle over the back and loin, or hollow areas behind and in front of the shoulder blades.
The Circle of Muscles
Movement begins in the hindquarters. The muscles that run from hip to stifle and down the front of the thigh bone (quadriceps, vastus, tensor fascia latae, and the iliopsoas), flex each hind leg in turn, pick it up, bring it forward during the “swing phase” of the stride, and set it on the ground (impact or grounding). The degree to which the hind leg reaches forward under the body is called “reach”. The farther the horse reaches under himself, the greater his power, speed, thrust, and balance control. This also affects the way he uses the rest of his body in movement. Good hind leg reach is the hallmark of a good athlete.
Once the hind leg is on the ground, the powerful muscles of the croup, hip, and the back of the hindquarters (the hamstrings, biceps femoris, semitendinosis and gluteals) tighten during the stance or support phase, straightening the hind leg and acting against the ground to push the horse’s body forward and upward, as the hoof breaks over and leaves the ground. This provides power and thrust at every stride.
The gluteal muscles of the hip tie into the long muscles of the back (longissimus dorsi and latissimus dorsi) and the deep muscles of the spine (multifidus). These in turn connect to the muscles of the top and sides of the torso and upper neck. They form a chain of muscles that goes all the way from the hind legs to the poll, on each side of the spine. At every stride, this upper muscle chain moves and stretches; we sit on it as we ride. Anything that interferes with this, such as a pinching saddle, an unbalanced rider, or hands that force the neck to stiffen and contort, can cause the horse to drop his back, making him stiff and hollow, and trapping his hind legs out behind so he cannot reach under himself. This is the most common cause of poor movement in ridden horses.
The Head, Neck and Jaw
The horse’s tongue attaches to the hyoid bone at the back of the jaw. At the back of the hyoid bone, a slender group of muscles (omohyoid and omothyroid) extends from the throat to the top of the forelegs, and connects to the breastbone and pectoral muscles. This muscle chain connects through the pectoral muscles and abdominal muscles to the pelvis – the “power plant” – creating a direct muscular connection between the horse’s mouth and his hind legs. When the horse stretches his head, neck and mouth, and chews softly, he is activating the “under muscle chain”. Fear or discomfort from severe bits, rough hands, or sharp teeth can all but paralyze a horse’s movement. In order to move well, a horse must have a relaxed, happy mouth and some degree of freedom to use his neck and head. Also, excessive tension on one rein inhibits the muscle chain, and therefore, the movement of the hind leg on that side.