Influence of the load of a rider or of a region with increased stiffness on the equine back: a modelling study

REASONS FOR PERFORMING STUDY: Knowledge of load effects is crucial for the understanding of the aetiology and pathogenesis of equine back problems. OBJECTIVE: To investigate different load scenarios of the equine back, such as being ridden or increased muscle tone, using biomechanical simulations. METHODS: Kinetic and kinematic data of 15 sound horses and the electromyelograph of their long back muscles were recorded. A biomechanical simulation model was used for simulations under different biomechanical scenarios (ridden/unridden, localised increased stiffness) using ADAMS. RESULTS: The vertical forces acting through a rider were: walk 3.83 N/kg, trot 5.18 N/kg and gallop 5.60 N/kg. No significant changes in transversal forces were found between ridden and unridden horses. Profound changes were seen in the torques at the segment following a region of increased stiffness: in walk, lateral peak torques increased from 342 to 1723 Nm, and in trot from 393 to 1004 Nm, and dorsoventral from 386 to 3705 Nm (walk) and 458 to 4340 Nm (trot). CONCLUSIONS AND POTENTIAL RELEVANCE: The simulation shows that the stress of a rider is lower than that of pathological processes such as partial increased stiffness of the back. Study of revised models with improved anatomical realism might help to raise the plausibility of model results.