Adaptations in equine appendicular muscle activity and movement occur during induced fore- and hindlimb lameness: An electromyographic and kinematic evaluation

Abstract

The relationship between lameness-related adaptations in equine appendicular motion and muscle activation is poorly understood and has not been studied objectively. The aim of this study was to compare muscle activity of selected fore- and hindlimb muscles, and movement of the joints they act on, between baseline and induced forelimb (iFL) and hindlimb (iHL) lameness. Three-dimensional kinematic data and surface electromyography (sEMG) data from the fore- (triceps brachii, latissimus dorsi) and hindlimbs (superficial gluteal, biceps femoris, semitendinosus) were bilaterally and synchronously collected from clinically non-lame horses (n = 8) trotting over-ground (baseline). Data collections were repeated during iFL and iHL conditions (2–3/5 AAEP), induced on separate days using a modified horseshoe. Motion asymmetry parameters and continuous joint and pro-retraction angles for each limb were calculated from kinematic data. Normalized average rectified value (ARV) and muscle activation onset, offset and activity duration were calculated from sEMG signals. Mixed model analysis and statistical parametric mapping, respectively, compared discrete and continuous variables between conditions (α= 0.05). Asymmetry parameters reflected the degree of iFL and iHL. Increased ARV occurred across muscles following iFL and iHL, except non-lame side forelimb muscles that significantly decreased following iFL. Significant, limb-specific changes in sEMG ARV, and activation timings reflected changes in joint angles and phasic shifts of the limb movement cycle following iFL and iHL. Muscular adaptations during iFL and iHL are detectable using sEMG and primarily involve increased bilateral activity and phasic activation shifts that reflect known compensatory movement patterns for reducing weightbearing on the lame limb. With further research and development, sEMG may provide a valuable diagnostic aid for quantifying the underlying neuromuscular adaptations to equine lameness, which are undetectable through human observation alone.

Adaptations in equine axial movement and muscle activity occur during induced fore‐ and hindlimb lameness: A kinematic and electromyographic evaluation during in‐hand trot

“…It has been suggested that compensatory longitudinal rotations of the back and pelvis during iHL are driven by increased activity of NLS epaxial, as well as HL protractor muscles. 46 The significant increases in NLS longissimus amplitude observed in this study, as well as NLS superficial gluteal, biceps femoris and semitendinosus observed in St. George et al 16 support the realisation of increased lateral bending of the back towards the NLS and of the pelvis towards the LS. Taken together, these findings are the first to support postulated muscular adaptations for known compensatory weightbearing and movement patterns of the limbs, back, and pelvis during hindlimb lameness.…”

“…Based on its anatomical location and attachments, it is thought to extend the spine when activated bilaterally in a concentric contraction, whereas unilateral concentric activation results in lateral bending and/or axial rotation. 16 Here, longissimus had a bilateral, biphasic activation pattern in each stride cycle, with each burst corresponding to the second half of HL stance, where thoracolumbar flexion occurs (Figures 1 and 5). This biphasic pattern is well-documented in sEMG studies of quadrupedal trot on a treadmill, 16,[35][36][37][38] with longissimus function generally attributed to eccentric activity that stabilises the thoracolumbar spine during passive flexion.…”

“…16 Here, longissimus had a bilateral, biphasic activation pattern in each stride cycle, with each burst corresponding to the second half of HL stance, where thoracolumbar flexion occurs (Figures 1 and 5). This biphasic pattern is well-documented in sEMG studies of quadrupedal trot on a treadmill, 16,[35][36][37][38] with longissimus function generally attributed to eccentric activity that stabilises the thoracolumbar spine during passive flexion. [37][38][39][40][41][42] Across these studies, there are both interindividual variation in activation timing 37,40,43 and variations in the number of activation bursts.…”

“…Longissimus is the largest equine epaxial muscle. Based on its anatomical location and attachments, it is thought to extend the spine when activated bilaterally in a concentric contraction, whereas unilateral concentric activation results in lateral bending and/or axial rotation 16 . Here, longissimus had a bilateral, biphasic activation pattern in each stride cycle, with each burst corresponding to the second half of HL stance, where thoracolumbar flexion occurs (Figures 1 and 5).…”

“…15 Unfortunately, axial movement was not quantified to corroborate this interpretation and comparisons were drawn from horses with subjectively assessed and nonstandardised lameness. In recognition of this, we have therefore initiated research to directly compare appendicular 16 and axial movement and muscle activity between nonlame and standardised lameness conditions during overground locomotion.…”