SMITH, L.E.; OLSEN, S.C.; DUTTO, D.J.; HOYT, D.F.; WICKLER, S.J.; California State Polytechnic Univ., Pomona; Pomona Collge, Claremont, CA: Do Forces Trigger The Trot-Gallop Transition?

It has been suggested that the mechanical trigger for the trot-gallop transition is a reduction in forces but some studies suggest that forces increase. The purposes of this study were to test the hypothesis that peak GRF at the transition from trot to gallop decreases, and to determine the effect of speed on peak GRF when galloping. Four horses were led at a trot or gallop over a force plate at a range of speeds, 3.0-6.0 m/s and 4.0-7.0 m/s respectively. Peak GRF in the forelimb increased with speed in both gaits. A regression of peak force on speed was performed on each animal�s data, and an ANOVA was performed on the slopes and on predicted GRF values at 5.0 m/s. Due to the small sample size, threshold for significance was set at P = 0.10. ANOVA indicated that the slopes were not different (P = 0.39), but the predicted values at 5 m/s were (P = 0.015). A Fisher�s PLSD test showed GRF for the leading forelimb to be 11% less (P = 0.082) than the trot and 18% less than the trail (P = 0.0047). Peak GRF in the hind limb did not change with speed. An ANOVA of mean values for each animal indicated GRFs were different (P = 0.086). Fisher�s PLSD showed that the leading hind limb exhibited an 11% increase (P = 0.048) and the trailing hind limb exhibited a 10% increase (P = 0.062) in peak GRF during the gallop. Impulse did not change with speed for any limb or gait. ANOVA of mean values indicated (P = 0.002) the net horizontal impulse in the lead limb was negative and lower than the trail limb (P = 0.027) and during the trot (P = 0.018). In conclusion, when a horse changes gait there is a net increase in GRF of 4% at the transition. When galloping, peak GRF increases with speed in the forelimb but not in the hind limb. This research was supported by NIH Grant S06 GM0539332 DFH & SJW.