Limb mechanics as a function of speed and gait: a study of functional strains in the radius and tibia of horse and dog.

Rosette strain gauges were attached to the midshaft of the radius and tibia of two horses and two dogs, which ran on a treadmill through their entire range of speed and gait. The relative magnitudes of the principal strains on the opposite cortices of each bone remained constant through the stance phase of the stride, and their orientation varied by a maximum of only 14 degrees through the entire speed range. The maximum strain rate increased linearly with speed, but the peak strain magnitude was also dependent upon the gait used, increasing incrementally by up to 59% at the transition from walk to trot, and dropping by 42% from a trot to a canter. Force transducers attached to the shoes of one horse indicated similar changes in ground load. The peak strains induced during vigorous activity are remarkably uniform in a wide range of animals. This suggests that the skeleton is scaled to provide constant safety margins between peak functional strains and those at which yield and ultimate failure occur.