Electromyographic and kinematic evaluation of movement and hindlimb muscle activity in horses with temporary forelimb lameness induction

Abstract

Introduction: Lameness is the most prevalent cause of occupational disability in horses, but limited information is available about adaptive muscle activity that facilitates movement during lameness. Forelimb (FL) lameness is known to provoke a secondary compensatory hindlimb (HL) lameness and it is hypothesised that this is reflected in HL muscle activity. The aim of this study was to compare Biceps Femoris (BF) muscle activity in horses before and after induced FL lameness using surface electromyography (sEMG).

Methods: Six clinically non-lame horses (5 mares, 1 stallion, age: 9.0±4.3 years, height: 160.7±4.6 cm, body mass: 581.5±47.4 kg) were used. sEMG sensors were attached bilaterally above BF. sEMG (2000Hz) and 3D kinematic (200Hz) data were synchronously collected from horses during in-hand trot trials, conducted on a hard runway before (baseline) and after FL lameness induction. Baseline data were initially collected, then temporary, mild FL lameness (2-3/5 AAEP) was induced and monitored by qualified veterinarians using a modified horseshoe (Merkens and Schamhardt, 1988). For stride segmentation, kinematic gait events were detected (Holt et al., 2017). To quantify lameness, MinDiff was calculated using poll vertical displacement data (Rhodin et al., 2018). Raw sEMG signals were DC-offset removed, high-pass filtered (St. George et al., 2018), and full-wave rectified. Integrated EMG (iEMG) was calculated using stride duration as temporal domain. iEMG from each horse were normalised to the maximum value observed for each HL across all strides from baseline condition. Difference between left and right iEMG values were calculated for each stride as a measure of muscle activity asymmetry (iEMGDiff). Repeated measures ANOVA compared iEMGDiff between conditions (baseline, induced FL lameness).

Results: Mean±sd MinDiff were baseline:-1.8±8.7 mm, left FL lameness induction:-55.3±34.1 mm, right FL lameness induction: 56.8±17.9 mm. Mean±sd iEMGDiff were 14.9±4.9 and 37.2±35.0 for baseline and FL lameness induction, respectively, but differences between conditions were non-significant (p=0.17, n2=0.34).

Conclusions: Compensatory pelvic movement is variable and less pronounced during FL lameness and high inter-individual iEMGDiff variability was observed. This may explain non-significant differences in BF muscle activity, but further research must confirm this.