Kinematic analysis has been used to understand performance in many sports, but few objective studies of equestrian technique have been published. The objective was to describe movements of the rider's torso and arms relative to movements of the horse's pelvis and shoulder and the position of the bit during trotting. Six experienced female riders rode the same dressage horse at a sitting trot, with rider and horse kinematics collected. The trot is a symmetrical gait, which implies kinematic symmetry between the first and the second halves of the gait. Three trials of a half stride, from left forelimb lift-off to right forelimb lift-off, were analysed for each subject. In all riders, trunk angle was maximal (backward tilt) in early stance, at which time the rider's hips were closest to and the rider's shoulders were furthest from the bit. Trunk angle was minimal (forward tilt) at the end of stance when the shoulders were closest to and the hips were furthest from the bit. Range of motion of the rider's hips and shoulders varied greatly between subjects. Movements of the rider's shoulder joint and elbow joint were synchronized with the trunk oscillations, so the distance from the rider's wrist to the horse's bit changed by only 15 ± 3 mm during the stride. It is concluded that the six experienced riders were able to accommodate the motion of the horse's body while maintaining a consistent contact with the bit by minimizing changes in the distance from the wrist to the bit.
We investigated the interaction between relaxation and contraction for remote, ipsilateral muscles of the hand and foot (wrist extensor/ankle dorsiflexor). Subjects sat in an armchair and were able to freely move their right hand and foot. They performed eight tasks: (1) wrist extension from a flexed (relaxed) position, (2) ankle dorsiflexion from a plantarflexed (relaxed) position, (3) wrist relaxation from an extended position, (4) ankle relaxation from a moderately dorsiflexed position. The remaining tasks involved (5) simultaneous performance of tasks 1 and 2, (6) 3 and 4, (7) 1 and 4, and (8) 2 and 3. Subjects performed each task as fast as possible after hearing a start signal. They were instructed not to activate antagonistic muscles in the tasks involving relaxation. When contraction of the wrist flexor/ankle dorsiflexor was concurrent with relaxation of the ipsilateral limb (ankle dorsiflexor/wrist extensor), the reaction time of contraction as observed in electromyography (EMG) activities in the wrist extensor/ankle dorsiflexor became longer and the EMG activities became smaller. Our findings suggest that muscle relaxation in one limb interferes with smooth movement of muscle contraction in the ipsilateral limb.
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