Body centre of mass movement in the sound horse

The body centre of mass (BCM) is a key factor in the analysis of equine loc omotion, as its position and movement determines the distribution and magni tude of loads on the limbs. In this study, the three-dimensional (3D) movem ent of the BCM in walking and trotting horses was assessed using a kinemati c, segmental method. Thirty markers representing 20 body segments were reco rded in 12 sound horses while standing, walking and trotting on a treadmill using a high-speed video system. Based on segmental inertial data, 3D posi tions of the segmental centres of mass as well as the total BCM were calcul ated. The position within the trunk during square standing and the movement s of the BCM were determined for the three planes. The position of the BCM in the standing horse is presented relative to exte rnal reference points. At the trot, vertical displacement amplitude of the BCM amounted to 53 (6) mm as mean (sd), which was 27% smaller than external trunk movement. Medio-lateral displacement amplitude of the BCM was 19 (4) mm, 34% less than trunk amplitude. Sagittal forward-backward oscillations of the BCM independent from general forward movement were 13 (3) mm, being 24% less than trunk movements. At the walk, vertical, medio-lateral and sag ittal BCM movements were smaller than trunk movements by 43, 65 and 65% res pectively. The results show reduced and efficient BCM movements compared to the trunk and form a basis for the assessment of various clinical conditions such as lameness, the influence of a rider and various dressage performances. (C) 2 000 Harcourt Publishers Ltd.