Horses are utilized for a wide variety of purposes, such as pleasure, work, and entertainment. Most people think of the racing Thoroughbred, reining Quarter Horse, or Grand Prix jumping warmblood as examples of athletic or working horses. But what about a horse working on a cattle ranch in Wyoming? Or the Amish horse utilized for transportation? Or how about draft teams tilling a field? All of these horses are considered working or athletic horses as well.

Any athletic event involving horses takes a certain amount of strength or endurance, in which muscles are continually contracting and relaxing in order to complete their job. This is defined as muscular work, the work done by muscles through the power of contraction. The amount of muscular work of which athletes are capable is dependent on the event's duration (distance) and its intensity.