Did you know your horse’s hock doesn’t just hinge like a door? Instead, as the hock bends, the cannon bone moves toward the midline of his body!
In this video I’m manipulating the hind left leg of the horse. You can see he has this incredible interlock between the tibiotarsal bone (the seashell shaped bit) and the bottom of the tibia. The angle of the tibiotarsal bone determines how dramatic this medial movement of the cannon bone truly is. I am exaggerating it slightly in the video (watch the tibia in my right hand) so you can see the movement clearly on film.
This medial-to-lateral-to-medial movement does make some sense. The hind legs are primarily for creating propulsive forwards motion. This movement during flexion allows the horse to move the hind legs closer to the midline of his body, then create a very slight outwards tension as he steps forwards.
To visualize how this might help, think of rollerblading. It’s extremely inefficient to simply move your legs forwards and backwards underneath your hips. Instead, thinking about pressing slightly to the outside can cause you to accelerate much faster, because the slight horizontal force provides you better traction against the ground, and allows the force to originate from beneath your center of mass.
However, overstraining this mechanism creates extreme torque on the limb. Lateral movements prior to proper strengthening, and even just a lengthened stride before a horse is ready, can cause this mechanism to work against the horse rather than for him. Did you know this was happening in your horse’s hock? Comment below!