Horses literally spend almost all their lives on their feet. Except for brief periods of laying down during certain sleep stages, they even sleep on their feet with legs locked. For an average-sized horse when standing still, each foot sustains 25 pounds per square foot (psi) of pressure continuously. When galloping, the horse sustains about 500 psi on the feet. That is slightly more than the pressure on a woman's stiletto heel and more than ten times the pressure on an elephant's feet. Because of the small size of the weight-bearing portion of the foot and the half-ton weight of the average horse, equine lameness is a significant risk.