Non-banked curved tracks influence movement symmetry in two-year-old Standardbred trotters.

Abstract

Little is known regarding how trotting through curves affects locomotion symmetry in Standardbred trotters. To investigate differences in objectively measured Standardbred trotter vertical motion symmetry between straight and non-banked, curved sections of oval trotting tracks during exercise warm-up, using a wireless inertial measurement unit (IMU) system. Cross-sectional, observational study. Sixteen horses were included. Mixed models were used to assess associations between symmetry, track segment (straight vs curve) and stride duration. Significant results for forelimb parameters were dependent on interactions between track segments and stride duration. At mean stride duration (0.611second), during the curved track segment horses showed a lower maximum vertical position of the head after push-off of the outside forelimb (estimate -2.3mm, P<0.0001, 95% CI -1.7 to -2.9) and higher minimum vertical position of the head during stance of the outside forelimb (estimate -1.8mm, P<0.0001, 95% CI -1.2 to -2.5) compared to straight track, mimicking outside forelimb impact and push-off asymmetry during track curves. For hindlimb parameters, during the curve there was a decreased downward motion of the pelvis during outer hindlimb stance (estimate-0.7mm, P<0.0001, 95% CI -0.4 to -1.0), mimicking outside hindlimb impact asymmetry. Horses were evaluated going in one direction only on the track (clockwise). Systematic differences between straight and curved track segments were found but did not fully correspond to previously described findings for horses lunged in circles. Effect sizes were overall small. Data in our study were collected from horses trotting on 1000m tracks with curve radii of 80-85m. On non-banked tracks of this size, collecting IMU symmetry data at jogging speeds without distinguishing between straight and curved parts is unlikely to adversely affect clinical decision-making.