JOHNSEN, D.A.J.; WICKLER, S.J.; COGGER, E.A.; HOYT, D.F.; California State Polytechnic University, Pomona: Kinematics of the Walk-Trot Transition in Horses

In humans, the transition from a walk to a run is correlated with changes in joint kinematics, in particular peak ankle angular velocity and peak ankle angular acceleration. Because the spring mass model describes both the run and the trot, we hypothesized that the walk-trot (W-T) transition in horses should also show differences in joint kinematics. In addition, time of contact (Tc) and step length in horses is shorter at the trot than the walk at transition speeds, which suggests a difference in kinematics at the W-T transition. The present study measured the hind limb kinematics of the W-T transition in the horse trotting and walking at transition speeds, 1.8 and 1.9 m/s, on a motorized treadmill. Horses were filmed at 125 Hz and the reflective joint markers were digitized. Peak ankle angular velocity and acceleration did not change with gait as expected. At transition speeds, the range of motion from contact to midstance (ROMc-ms) of the hip and the knee tended to be lower in trotting than walking. At the ankle, ROMc-ms showed no change, while at the metacarpophalangeal (MP) and the interphalangeal joints it was larger during the trot than the walk. The hip ROM during all of stance was smaller at the trot, but no change was seen at the other joints. The shorter Tc at the trot likely causes this reduced motion of the hip. The smaller hip and knee ROM suggest less leg compression at the trot, and the observed increase in the ROM of the MP suggests an increase in peak ground reaction force. Together these observations indicate an increase in stiffness of the leg when transitioning from a walk to a trot. (Supported by NIH S06-GM53933 to DFH &SJW and an Agricultural Research Initiative grant)