FERRIS, A.E.*; HOYT, D.F.; DUTTO, D.J.; COGGER, E.A.; WICKLER, S.J.; Calif. St. Polytechinc Univ., Pomona: Dynamics of the equine forelimb during landing from a jump: A pilot study

A successful jump requires not only clearing an obstacle, but also landing safely. The first limb to strike after clearing a 1.3 m obstacle produces a large vertical ground reaction force and a net horizontal propulsive force. Meershoek reported a large flexor moment at the metacarpophalangeal joint (MCP) joint during landing, similar to our unpublished results during trotting when we also observed that the MCP did net positive work. It has been suggested that there is a transfer of energy from the proximal joints to the MCP resulting in net positive work. It is hypothesized: that this limb will produce net positive work because of the propulsive forces previously reported; the majority of the positive work will be done by the shoulder; the elbow will do negative work. Two horses were hand-lead and jumped over a 0.6 m obstacle. The landing on a force plate (1000 Hz) was recorded with a high-speed digital video camera (250 Hz) for inverse dynamic analysis of moments, power and work for each joint. Peak vertical ground reaction forces were 11.9 � 0.7 N�kg-1. Horizontal ground reaction forces were similar to those previously reported. Net horizontal impulse was propulsive (0.19 � 0.02 Ns�kg-1). Net work of the forelimb was positive (0.12 � 0.02 J�kg-1) with the shoulder doing the most positive work (0.27 � 0.05 J�kg-1). The MCP did a small amount of net positive work (0.06 � 0.01 J�kg-1). The elbow (-0.18 � 0.01 J�kg-1), carpus (-0.01 � 0.00 J�kg-1), and distal interphalangeal joint (-0.02 � 0.00 J�kg-1) did net negative work. During the last ca. 30% of stance the elbow extends, an action that could increase the positive work appearing at the MCP through the action of multiarticular tendons connecting the humerus to the distal phalanx.