Locomotor mechanics of the tolt in Icelandic horses

Objective-To evaluate the locomotor mechanics of the tolt in Icelandic horses. Animals-10 adult Icelandic horses with no history of lameness. Procedures-Force platform data were captured for 27 trials for horses ridden at a tolt in a lateral sequence single-foot gait at a steady speed from 0.89 to 5.98 m/s. Simultaneous kinematic data were obtained by tracking retroflective markers overlying the right fore- and hind limbs. These kinetic and kinematic data were combined to evaluate 3 mechanical approaches, duty factor, Froude number, and center of mass (COM) mechanics, and to evaluate the capacity to recover mechanical energies during tolting via inverse pendulum and spring-mass (bouncing) mechanics. Results-Tolting horses had in-phase fluctuations of gravitational potential and kinetic energies of their COM and a capacity to recover mechanical energy through elastic recoil of spring elements in their limbs. These characteristics, along with Froude numbers exceeding values expected for the walk-run transition, are indicative of bouncing mechanics and, hence, most strongly ally tolting with running. Only the footfall pattern of a lateral sequence single-foot gait and low vertical excursions of the COM are more commonly associated with walking. Conclusions and Clinical Relevance-At the tolt, horses have unique mechanical characteristics that should be understood for veterinary care. Differences in interlimb coordination between tolting and trotting mask the overall similarities in most other aspects of their locomotor dynamics.