Researchers in New Zealand used limb measurements obtained by CT examinations and limb dissections along with kinematic data obtained while trotting and cantering Thoroughbred racehorses over uneven ground to develop a model of how structures in the limbs respond to changes in the ground surface. They examined joint movements, muscle-tendon strains and ligament strains.

Five Thoroughbred racehorses were exercised at a trot and a canter over a simulated track surface that was modified to be harder than usual, typical in hardness and softer than usual. The kinematic measurements and modeling was designed to estimate the effects during the weight-bearing portion of the stride over the modified surface, as well as during the swing phase of the subsequent stride. They hypothesized that the horses’ gait would be affected in the stride following the stride on top of the irregular surface.

In response to the harder ground surface, the proximal limb was more compliant at the trot and canter with increased shoulder flexion in the first stance phase followed by increased elbow and carpal flexion in the subsequent swing phase. The suspensory ligaments and their muscle-tendon units were less strained while strains in the opposing lacertus fibrosus (long bicep tendons) were increased. At the trot on the irregularly soft ground, the coffin joints were more flexed and the elbows more extended resulting in increased strain in the deep digital flexor tendons, extensor branches and lacertus fibrosus. At the canter the coffin joint was more flexed and the fetlock less hyperextended with less…