When trotting on a circle, the fore and hind limbs on the outside carry more weight than those on the inside. On small circles and/or at fast speeds, this asymmetry gives the appearance of lameness in the limbs on the inside of the circle. | Photo: Courtesy Dr. Hillary Clayton

Horses generate ground reaction forces (GRF) when they press their hooves against the ground to produce locomotion. One world-renowned researcher in equine locomotion and biomechanics says recognizing these invisible forces is key to understanding how horses move and how they compensate for lameness.

As one of the keynote speakers at the 2019 Equine Science Society Symposium, held June 3-6 in Asheville, North Carolina, Hilary Clayton BVMS, PhD, Dipl. ACVSMR, FRCVS, of Sport Horse Science, in Mason, Michigan, described GRFs and how they change with different movement patterns and lameness.

Ground reaction forces act in various directions and can be affected by the horse’s body weight, gait, speed, shoeing, and footing, said Clayton. Researchers study the vertical, longitudinal, and transverse components of GRFs to understand how they affect movement and performance. You see vertical GRFs, for instance, when horses jump over obstacles; longitudinal GRFs when horses gallop; and transverse GRFs when horses pivot and turn sharply, she explained