Is sEMG a repeatable measure of muscle activity in horses – between-day repeatability at in-hand trot

Abstract

The repeatability of surface electromyography (sEMG) is an important consideration for its potential clinical application in equine gait analysis. We hypothesize that equine sEMG profiles are repeatable between measurement sessions, but this has not been demonstrated. Thus, we evaluated the between-day repeatability of normalised sEMG activity profiles, from triceps brachii (triceps), latissimus dorsi (latissimus), longissimus dorsi (longissimus), biceps femoris (biceps), superficial gluteal (gluteal) and semitendinosus in n=8 clinically non-lame horses. sEMG sensors (Trigno, Delsys Inc.) were bilaterally located on muscles to collect data during in-hand trot on two occasions (day 1: 3.11±0.23 m/s, day 2: 3.07±0.35 m/s) with a minimum 24-hour interval. Raw sEMG signals from ten trot strides per horse and day were DC-offset removed, high-pass filtered (40 Hz), full-wave rectified, low-pass filtered (25 Hz), and normalised with respect to peak amplitude and percent stride. Within-subject, ensemble average sEMG profiles across strides from each muscle and day were calculated. The adjusted coefficient of multiple correlation (CMC) was used to evaluate the between-day repeatability of ensemble average sEMG profiles and tends to 1 when waveforms are similar. Bilateral gluteal, semitendinosus, triceps and longissimus (at T14 and L1) and left biceps showed excellent between-day repeatability with group-averaged CMCs>0.90 (range 0.90- 0.97). Bilateral latissimus and right biceps showed good reliability with group-averaged CMCs>0.75 (range 0.78-0.88). The sEMG profiles studied here are consistent across days, suggesting that it is reasonable to use sEMG to objectively monitor the activity of these muscles across multiple gait evaluation sessions at trot.