Kinematics and kinetics of the carpus.

This study investigated the kinematics and kinetics of the carpus during the stance phase. Five Standardbred horses trotted on a treadmill at 8.9 m/s. The kinematics of the horses were filmed and hoof reaction forces (HRF) were recorded. The carpus was overextended throughout most of the stance. There were 2 periods of overextension, a more rapid period in the beginning of the stance and second directly following the first period. Maximal overextension occurred slightly before the second minimum of the braking horizontal HRF. The metacarpal and antebrachial segments rotated counter-clockwise for most of the stance. The angular velocities of these segments attained absolute and local extremes that were concurrent. The absolute maxima in the longitudinal and the transversal acceleration of the proximal metacarpus were coincident in time with the minimal horizontal braking force. The moment of force about the carpus was extending throughout most of the stance, with a short period of flexion near the end of the stance. The results show that horizontal braking of the hoof results in impulsive loading followed by maximal overextension of the carpus. The second phase of overextension is suggested to be related to the tension or active roll of the flexor tendons of the distal limb. The carpus is, therefore, subjected to rapid and high loading in both the longitudinal and transversal directions, as well as large moments and forces.