HOYT, D.F.*; WICKLER, S.J.; COGGER, E.A.; GOEHRING, M.E: A Reexamination Of The Trot-Gallop Transition: Insights From The Study Of Locomotion On An Incline.

Previous workers concluded that forces trigger the trot-gallop (T-G) transition because it occurred at a lower speed when ponies carried a load and, at the T-G speed, the metabolic rate was higher galloping than trotting. We determined how incline (which does not increase force) affects the T-G transition speed in 6 horses (mean mass 460 kg) trained for at least 6 months to run on a treadmill on the level and up a 10% incline. First, transition speeds (the lowest speed at which the horse would gallop continuously for one minute) were determined by changing speed in increments of 0.25 m/s. Subsequently, the horses were trained to change gait on command over a range of speeds from 1.0 m/s below T-G speed to 0.5 m/s above. Metabolic rate was measured using open-flow respirometry. Duty factor (DF) was determined using accelerometers taped to the horses’ hooves. Accelerometer signals were validated with high-speed (125 hz) video. For trotting, data from a diagonal pair of legs were averaged and for galloping data from all four legs were averaged. Statistics reported are for paired t-tests. On an incline, the T-G speed is 0.75 m/s slower (p<0.001), suggesting that force is not the trigger. At the highest trotting speed, DF on the incline is 6% higher (p=0.018) than on the level, suggesting that peak ground reaction forces may be lower on the incline and there may not be a consistent threshold. At the T-G speed on the level, metabolic rate is 7% lower (p=0.009) galloping than trotting and at the T-G speed on the incline (5.08 m/s) there is no difference in metabolic rate (p=0.09), indicating metabolism may be the trigger. Under both conditions DF at the T-G speed is lower when galloping than trotting.