High-pass filtering (HPF) is a fundamental signal processing method for the attenuation of low-frequency noise contamination, namely baseline noise and movement artefact noise, in human surface electromyography (sEMG) research. Despite this, HPF is largely overlooked in equine sEMG research, with many studies not applying, or failing to describe, the application of HPF. An optimal HPF cut-off frequency maximally attenuates noise while minimally affecting sEMG signal power, but this has not been investigated for equine sEMG signals. The aim of this study was to determine the optimal cut-off frequency for attenuation of low-frequency noise in sEMG signals from the Triceps Brachii and Biceps Femoris of 20 horses during trot and canter. sEMG signals were HPF with cut-off frequencies ranging from 0 to 80 Hz and were subjected to power spectral analysis and enveloped using RMS to calculate spectral peaks, indicative of motion artefact, and signal loss, respectively. Processed signals consistently revealed a low-frequency peak between 0 and 20 Hz, which was associated with motion artefact. Across all muscles and gaits, a 30-40 Hz cut-off fully attenuated the low-frequency peak with the least amount of signal loss and was therefore considered optimal for attenuating low-frequency noise from the sEMG signals explored in this study.

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1The design of a novel apparatus, the Glen Withy torque tester (GWTT), for measuring 2 horizontal shear properties in equine sport surfaces is described. Previous research has 3 considered the effect of vertical loading on equine performance and injury but only limited 4 discussion has concerned the grip or horizontal motion of the hoof. The horizontal support of 5 the hoof by the surface must be sufficient to avoid excess slip without overloading the limb. 6The GWTT measures the torque necessary to twist an artificial hoof that is being pushed into 7 the surface under a consistently applied vertical load. Its output was validated using a steel 8 surface, then was used to test two sand and fibre surfaces (waxed and non-waxed) through 9 rotations of 40-140°, and vertical loads of 156-980 N. An Orono biomechanical surface 10 tester (OBST) measured longitudinal shear and vertical force, whilst a traction tester 11 measured rotational shear after being dropped onto the surfaces. A weak, but significant, 12 linear relationship was found between rotational shear measured using the GWTT and 13 longitudinal shear quantified using the OBST. However, only the GWTT was able to detect 14 significant differences in shear resistance between the surfaces.

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This study proposes a simple kinematic method of detecting hoof-on, hoof-off and GRFz at walk, trot and canter. Further work should focus on validating the methodology in a larger number of horses and should extend the method for use on surfaces with varying levels of compliance.