Biomechanical findings in horses showing asymmetrical vertical excursions of the withers at walk.
Authors: Byström Anna, Egenvall Agneta, Roepstorff Lars, Rhodin Marie, Bragança Filipe S, Hernlund Elin, van Weeren René, Weishaupt Michael A, Clayton Hilary M
Journal: PloS one
Summary
# Asymmetrical Withers Movement in Sound Dressage Horses: A Biomechanical Perspective Withers asymmetry during walk—where one side drops lower than the other—has been observed clinically in horses judged as sound, yet the underlying biomechanical mechanisms remain poorly understood. Researchers recorded seven high-level dressage horses walking on an instrumented treadmill whilst simultaneously capturing limb kinematics and vertical ground reaction forces, allowing them to correlate withers height variations with detailed spatiotemporal and loading data across multiple strides. The study revealed substantial withers asymmetry (ranging from 0.3 to 23 mm difference between contralateral steps), predominantly manifesting as preferential dropping on one side during forelimb stance; crucially, this asymmetry correlated with increased forelimb retraction distance and shortened stance duration on the side where maximum withers drop occurred, plus increased hind limb protraction–retraction range and lateral haunches displacement, but *not* with differences in vertical loading between forelimbs. These findings suggest that withers asymmetry in clinically sound horses reflects a laterality-driven postural pattern rather than weight-bearing compensation, indicating that such asymmetries may be normal functional variants rather than necessarily pathological. For practitioners, this implies that minor withers asymmetry observed during trotting examinations should not automatically be interpreted as lameness or limb dysfunction; however, the biomechanical complexity involved warrants careful assessment of the entire kinetic chain to distinguish functional asymmetry from genuine pathology.
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Practical Takeaways
- •Asymmetrical withers movement at walk is common in sound horses and does not necessarily indicate lameness or pathology; it may reflect natural laterality and movement preferences.
- •Farriers and veterinarians should not automatically interpret withers asymmetry as a sign of pain or loading problems—assess the horse's overall movement quality, performance, and clinical signs before making interventions.
- •Use of force plate and motion capture can help distinguish true biomechanical compensation (asymmetrical loading) from inherent movement asymmetry (laterality patterns), informing whether corrective work or treatment is needed.
Key Findings
- •Withers asymmetry at walk ranged from 0.3–23 mm in seven sound dressage horses, with five showing consistent left-side preference and one showing right-side preference.
- •Forelimbs with greater retraction at toe-off and shorter stance duration were associated with increased withers asymmetry (1 mm retraction increase predicted 0.17 mm asymmetry increase).
- •Hind limbs with greater range of motion during stance were associated with increased withers asymmetry (1 mm increase predicted 0.2 mm asymmetry increase).
- •Vertical ground reaction forces between forelimbs were non-significant, suggesting asymmetry reflects inherent laterality rather than weight-bearing lameness.