Why Is the Horse Such a Superior Athlete?

Much of the explanation of why horses can run so fast for so long is tied to their status as prey animals. Horses are well equipped to flee from danger (real or perceived) rather than to fight off a predator. The equine respiratory and circulatory systems are superbly designed to maximize the horse’s ability to support intense exercise.

A healthy horse at rest has a respiratory volume of about 150 liters per minute. During intense exercise, the horse’s respiratory volume can rise to as much as 1,500 to 1,800 liters per minute, an increase of ten times or more. This ability of the horse to exchange oxygen and carbon dioxide is important in allowing the horse to continue strenuous exercise for a long period of time.

Heart rate in exercising horses can increase 7 to 8 times over their resting rate. In comparison, the human heart rate during exercise rises to only 4.2 to 4.4 times the resting rate. Horses have another circulatory system advantage that humans lack. In horses, much of the red blood cell volume is stored in the spleen while the horse is idle or moving at a slow speed.

When the horse begins to exercise strenuously, the spleen contracts, sending these stored red blood cells into circulation and greatly increasing the horse’s ability to carry oxygen to working muscles. Thus, VO2max (the maximum ability to use oxygen) has an increase in the exercising horse of 40- to 110-fold, whereas the rate of increase in exercising VO2max in humans is only about 13- to 23-fold.