FERRIS, A.E.*; DUTTO, D.J.; HOYT, D.F.; CLAYTON, H.M.; COGGER, E.A.; WICKLER, S.J.; Calif. State Polytechnic Univ., Pomona 91768; College of Veterinary Medicine, Michigan State University, East Lansing, MI 48854: Joint kinetics of the horse during trotting: the forelimb during stance

During trotting, the vertical ground reaction force generated by the forelimb increases with increasing speed from 2.5 to 5 m/s. Does the mechanical work produced by the forelimb also increase in this speed range? Synchronized ground reaction force (1000 Hz) and digital video (250 Hz) were recorded while horses trotted at a constant speed on a runway. Inverse dynamic analysis was used to determine the joint moment, power, and work generated during the stance phase of trotting for the joints of the forelimb of 4 horses: shoulder, elbow, carpus, metacarpophalangeal (MCP), and distal interphalangeal (DIP). The DIP, MCP, and carpus produced flexor moments through most of stance (peak values: -0.3 � 0.2, -1.3 � 0.3 and -1.3 � 0.3 Nm/kg, respectively). Elbow and shoulder joints produced either extension or flexion moments depending on the period of stance (peak extensor moments: 1.1 � 0.3 and 1.5 � 0.4 Nm/kg, respectively). Most of the peak moments tended to increase slightly with speed for all 5 joints, indicative perhaps of increased musculoskeletal loading with increased speed. Peak positive power tended to increase with speed for the shoulder and MCP, while peak negative power increased for the elbow and fetlock. Peak power did show a proximal to distal timing as the shoulder and elbow peaked at 44%, the carpus at 60%, the MCP at 67%, and the DIP at 79% of stance, consistent with an energy flow from proximal to distal. Forelimb net work was small and independent of speed (0.06 � 0.11 J/kg), with the shoulder providing the most work (0.11 � 0.07 J/kg). It appears that the forelimb provides little mechanical work to support trotting. Supported by NIH # S06 GM53933 to DFH & SJW.