The effect of trotting speed on the kinematics of head, withers and pelvis

Quantitative kinematic gait analysis is gaining popularity in equine practice. It allows for objective quantification of motion symmetry, which can be used to quantify the effect of nerve blocks and flexion tests. This approach is mainly based on measurement of motion symmetry of the vertical displacement of head, withers and pelvis. The objective of this study was to evaluate the effect of trotting speed on kinematic symmetry parameters in a group of horses perceived to be sound by their owner. Thirty-six horses were equipped with reflective spherical markers on the poll, withers and tuber sacrale. After an acclimatisation period to treadmill locomotion, horses were trotted on the treadmill at increasing speeds up to their individual breaking speed at increments of 0.4 m/s. Kinematic gait analysis was performed using 3D optical motion capture. The effect of speed on several kinematic parameters was tested using mixed models with significance set at p <0.05. For the head, increased speed resulted in a significant reduction of the asymmetry parameter vector sum (VS) (P<0.001) and a decrease in the range of motion (ROM) of the vertical displacement (P<0.001). For the withers, the effect was a decrease of the withers VS (P<0.001) and an increase of ROM (P<0.001). For the pelvis, an increase of speed resulted in a reduced ROM (P<0.001), but no significant effect was found for the pelvis VS (P=0.7). Speed has a significant effect on important kinematic parameters used for objective lameness assessment. Speed between repeated measurements should, therefore, be maintained as constant.