The biomechanical construction of the horse's body and activity patterns of three important muscles of the trunk in the walk, trot and canter.
Authors: Kienapfel K, Preuschoft H, Wulf A, Wagner H
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Understanding how trunk muscles stabilise the equine spine during movement has largely been overlooked in clinical practice, despite their critical role in maintaining posture and transmitting forces between limbs and torso. Kienapfel and colleagues used surface electromyography synchronised with accelerometers to map activity patterns in the rectus abdominis, external oblique, and longissimus dorsi across walk, trot and canter in five horses, both ridden and unridden, analysing ten consecutive stride cycles per gait to establish precise timing of muscular recruitment. Their findings revealed that trunk muscles remain relatively quiet during walk but become substantially active during trot and canter, particularly when vertical acceleration reaches twice gravitational force during diagonal support phases—at these moments the rectus abdominis fires maximally to resist bending moments, whilst the external oblique engages asymmetrically to counteract torsional forces, with the ipsilateral longissimus dorsi stabilising the lumbar spine against hip flexion forces from the hind limbs. These biomechanically predicted patterns were confirmed precisely by the EMG data, providing objective evidence that effective trunk stability depends on coordinated, load-responsive activation of deep core muscles. For practitioners, this validates the importance of conditioning exercises targeting trunk strength and proprioception, and suggests that asymmetrical or delayed activation patterns in these muscles could contribute to back problems, gait irregularities, and poor performance.
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Practical Takeaways
- •Understanding trunk muscle activation patterns across gaits can inform saddle fit and rider positioning to avoid interference with natural muscle function, particularly during trot and canter
- •Asymmetrical oblique muscle activity highlights the importance of balanced ridden work and may be relevant to managing horses with unilateral trunk muscle tension or asymmetry
- •The critical role of trunk stabilizers in dynamic movement suggests that core conditioning exercises should be incorporated into training and rehabilitation protocols
Key Findings
- •Rectus abdominis muscle shows greatest activity during diagonal support phases in trot and canter when vertical acceleration reaches two times earth acceleration
- •External oblique muscles activate asymmetrically during torsional and bending moments, with contralateral internal obliques providing stabilization on the opposite side
- •Ipsilateral longissimus dorsi activates during hindlimb ground contact in trot and canter to stabilize the lumbar spine and hip joint against flexion forces
- •EMG activity patterns in trunk muscles directly confirm biomechanical predictions from theoretical static analysis of equine trunk mechanics