Article written by Kirsty Davis EQ ITEC Dip, MESMA, ITEC Dip Hu
The Jumping Take off:
Every muscle in the body will be performing to some extent in every movement.
In the take off for the jump we see here some very specific muscles doing the bulk of the work for both horse and rider. Although the rider is largely concerned with balance, his quads and hamstrings are working isometrically (working without shortening or lengthening) and his peroneus is working in the same way to keep the lower leg close to the horses side.
For the horse, his back muscles are extending the back and the massive propulsive energy is about to be released from the gluteal mass which extends the hip joint, the femur opens out to the rear in relation to the pelvis. This is further enhanced by the hamstring group which have complex actions but largely extend the limb (pull back), for instance when the horse stretches his leg out behind him, but when the hoof is planted on the ground this action then turns into explosive propulsion. As the horse has not only pushed his front end of the floor but also lifted it of the floor, the propulsion sends him airborne.
This photo shows the typical biomechanical positioning of the hindquarters to set up elastic recoil (think of a catapult being drawn back) and optimise the effect of the extensor muscles of the hindlimb to create propulsion. In this position the hamstrings are momentarily also stabilising the horse as he lifts his forehand into the air. You now start to appreciate the very complex multiple actions and reactions of these tissues.
Ground conditions have a impact on the effect of the muscles. If the ground is firm propulsion is far easier, as the ground exerts a force against the planted hoof, maximising effect. In reverse, deep ground diminishes the propulsion of the horse. Less of the propulsive energy is passed through the horse, some of the energy transfered to the ground is lost through the movement of the ground away from the horse on take off. Similarly, if the ground is slippery. There is also the added danger that at the moment this photo is taken if the hindlimbs slip forwards while the hamstrings are compressing, the hamstrings will tear to a greater or lesser extent.
Another interesting adaptation the horse has developed very well over millenia is the biomechanical success that is ‘elastic recoil’. On this diagram you can see the soleus (which works along side the gastrocnemius, equivalent to our calf muscles) attached to the point of hock via the Achilles tendon. This unit’s fibres extend and are part of the tendinous and ligamentous tissues beneath the hock. As the horse lowers onto his pasterns he puts himself in a position that stretches these fibres and much like a rubber band ‘elastic energy’ is stored up and like the rubber band, it has the ability to propel.
Kirsty Davis EQ ITEC Dip, MESMA, ITEC Dip Hu
Photos by Katie Mortimore
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