Jumping (horse)

Jumping plays a major role in many equestrian sports, such as show jumping, fox hunting, steeplechasing, and eventing. The biomechanics of jumping, the influence of the rider, and the heritability of jumping prowess have all been the focus of research.

The airborne phase of the jumping process occurs between stance phases of the fore and hind limbs and is therefore biomechanically equivalent to a highly suspended or elevated canter stride. For this reason, horses typically approach obstacles at the canter. The jumping process can be broken down into five phases:

The "approach" is the final canter stride before the jump, during which the horse places all four legs for the optimal take-off. The horse reaches forward and down with his neck to lower the forehand and his center of mass. The forelegs are propped or strutted out in front of the body. This relatively sudden braking action allows momentum to carry the hindlegs further under the body of the horse than would be otherwise possible. While the action is more fluid, it is mechanically similar to the act of crouching down before jumping.

The "take-off" begins when the forelegs leave the ground and is completed when the hindlegs leave the ground. Once the horse leaves the ground, he is unable to influence the trajectory that his center of mass follows through the air, which makes take-off the most critical phase of the jumping process. Most of the energy required to clear an obstacle is produced by the hind legs. The longer the hindlegs are in contact with the ground, the greater their capacity for producing power; the further forward the hindlegs are placed under the body, closer to the obsctacle, the longer this stance phase. Power is produced by the compression of the hindleg, which flexes at the hip, stifle, hock, and fetlock, and then releases energy like a spring.

During "flight", the horse's center of mass follows a parabolic trajectory over which it has no control. The horse can change the position of its legs and body in relation to the center of mass, however, which is critical to clearing an obstacle safely. The horse's body rotates through the air, a quality called "bascule", to ensure that while the forehand clears the fence, the shoulders are the highest point of the body, and while the hind end clears the fence, the hips are the highest point of the body. The bascule is the horse's arc over the fence. A horse with a good bascule makes a rounded jump and helps the horse jump higher. The forelegs are drawn up towards the body and the hindlegs are "retroflexed" out away from the body to clear the obstacle. During flight, the rider has little impact on the actual trajectory of the horse's body. Foals frequently change leads when jumping.

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