Concussion forces – The muscles of the horses back disperse the forces of concussion from the horse’s motion. The horse’s foot lands with its heel first, think of it like a landing airplane, then it transfers to the front portion. This appears to be the most efficient function of the loaded foot as it is two phase to assist with the force of concussion and therefore acts as a shock absorber which then transmits the force up through the column of the leg.
The forelimbs forces travel up and backwards terminating at the lumbo-sacral junction just behind the saddle, the hind limbs travel upwards through the gluteal and terminate at the 4th and 5th vertebrae in the neck. This is why the spinal vertebrae alignment and healthy musculature surrounding it is important to enable the vertebrae to cope with the forces put on it.
The horse is not fully mature until 5 years old, it is especially worth bearing in mind that the growth plates along the horses spine do not fuse until this time therefore carrying weight can have a detrimental effect and cause sprains, for instance displacing a vertebral growth plate therefore this is something absolutely worth considering when backing and working a young horse.
Locomotion is a result of generated forces as the hooves push against the ground which determine direction and speed, the harder the push the faster the movement and speed.
When the hooves push against the ground the horses body moves in the opposite direction:
It is worth remembering that the hind limbs are the engine propelling the force forwards to the forehand and the fore limbs turn and adjust the speed very much like a rear wheel drive car.
Each limb has a support phase when the hoof is on the ground and a flight phase as it swings forward. Although the flight phase is most noticeable it is the support phase which is most important, we want to see a lot of flexion maintained. As the horse develops more strength through its muscles it can push from its hoof more rapidly and this means the hoof is less in contact with the ground which in turns gains expression as the horse becomes quicker behind.
As the horses self carriage develops the back muscles work in unison to lighten the forehand. The long longissimus muscles either side of the spine assist in lifting the forehand. The sling muscles also engage producing an uphill frame. The thoracic sling muscles, Serratus ventralis and pectoral muscles run from the inner surface of the scapula and humerus to the ribs and sternum. Upon relaxing and lengthening through these muscles the ribcage lowers between the shoulders, when the muscles contract and shorten this lifts the rib cage which in turn raises the withers giving an uphill appearance. This is crucial to self carriage.
The horses gut can weigh 50 gallons and hangs from the spine, much of the internal organs are suspended from the bottom of the vertebrae with a ligament and rest on the floor of the abdomen. The majority of the gut weight is helped by the rectus abdominus muscle under the belly.
The rectus abdominus muscle and the topline muscles have to work together to lift the spine and abdomen when carrying weight above it. If these muscles aren’t working together the horse hollows its back and develops a sunken abdomen.
The head and neck are very much connected to the push of the hooves on the ground. Dressage horses that are not yet strong enough through their backs to use the long back muscles to lift the forehand compensate by raising their head and necks with the support phase, just as with a lame horse the head is lifted as the weaker forelimb pushes off to assist in lifting the forehand.
Written by Sam Jamieson © 2015