Kinematics of the hind limb push‐off in elite show jumping horses

Abstract

Summary The sagittal plane kinematics of trunk, neck, and hind limb were analysed in a group of 15 elite show jumping horses during the push‐off of the hind limbs before jumping a 1.50 m upright fence. Similar movement patterns were observed in all horses. Ensemble averages of the kinematic variables of the group were calculated after spline smoothing and time‐normalisation with respect to the support phase. The final support phase of the hind limbs was symmetrical and had a duration of 221 ± 19 ms. During the first half of this period, the trunk rotated towards a more upright orientation and the height of the estimated centre of mass was decreased by about 0.05 m. These movements were accompanied by 25 degrees of hip extension and 40 degrees of flexion in the stifle and hock joints. These movements bring the hind limbs into a favourable, flexed position to produce mechanical power and transfer it to the trunk. Maximal flexion in the tarsal joint was reached at 98 ms after ground contact, followed by the stifle joint at 124 ms. After maximal flexion, the total extension movement of the tarsal and stifle joints was 45 and 22 degrees respectively. The extension of the hip continued until 152 ms after ground contact, and the angle remained stationary afterwards. The extension of the hind limb was accompanied by a large increase in horizontal and vertical velocity of the trunk, and a reversal of the rotation of the trunk. The average rate of mechanical power production during the entire push‐off, estimated from the change in kinetic and potential energy, was 59,000 W. By comparing total energy at the beginning and end of the support phase, it was concluded that most of the energy required to clear the fence was produced by the hind limbs during the final support phase, and that the previous actions of the forelimbs are merely bringing the horse into a good position for the final push‐off.