Title:
Contribution of dynamic calibration to the measurement accuracy of a pressure plate system throughout the stance phase in sound horses.

Abstract:
The aim of this study was to evaluate the accuracy of the vertical force curve of a pressure plate (PP) using dynamic calibration with a force plate (FP) in six sound Warmblood horses. The animals were walked and trotted over a combined PP-FP system sampling at 250 Hz. Five valid measurements of each forelimb were collected. The recalibration factor (RF), the ratio between the calibrated and raw PP data, was evaluated in each timeframe throughout the stance phase. Following dynamic calibration, the vertical force curve of the PP demonstrated a characteristic biphasic pattern at the walk and typical spikes at the beginning and end of stance at the trot. Both at walk and trot, the RF was considerably higher and more variable in the first 5% of stance (i.e. the impact phase) and during the final 20% of stance (i.e. the breakover phase), whereas between these phases (i.e. in the support phase), the RF was lower and remained relatively constant. These findings were confirmed by plotting the RF as a function of the vertical force and the RF in the loading part of the vertical force curve was lower than in the unloading part of the curve. Without dynamic calibration with a FP, the accuracy of the PP appears suboptimal, especially at the impact and breakover phases. However, the accuracy of the PP was relatively high and constant during the support phase, and higher loading was not associated with increasing deviation. It is therefore essential to optimise PP calibration, as this may downsize systematic measuring errors. However, in a clinical setting, where a stand-alone PP is used to objectively quantify locomotor symmetry, these errors can be readily eliminated by evaluating left:right symmetry ratios.