How the horse moves: 1. Significance of graphical representations of equine forelimb kinematics

Kinematic data of the equine hind limb are presented graphically and related to functional aspects of the hind limb in locomotion. The trot of 24 two-year-old Dutch Warmblood horses was recorded at 4 m/s on a high-speed treadmill using kinematic analysis equipment. Joint angle-time, angle-angle, stick and marker diagrams were used to present graphically the data following standardised procedures. As the kinematic data were expressed with reference to the joint angles of the horse standing squarely and were time-standardised to the duration of the stride cycle, mean joint curves for the total group could be calculated and therefore describe the function of the different segments of the equine hind limb. The motion of the hind limb in the sagittal plane appeared to be pendular around a rotation point in the acetabulum. During the stance phase the extension of the fetlock joint and stance flexion of the stifle, tarsal and coffin joints illustrate the shock absorption of the hind limb. In the swing phase the reciprocal apparatus, which forms the coupling mechanism between stifle and tarsal joint, also influences the fetlock joint because synchronous flexion and extension between these 3 joints were demonstrated. By graphically presenting hind limb motion we were able to illustrate the relation between kinematics and function. This graphic analysis can be used in clinical studies involving quantification of equine hind limb coordination in the sagittal plane.