Optimal nutrition of the performance horse hinges foremost on the exercise it performs. Just as the diet of a human bodybuilder is dissimilar to that of a marathon runner, most horses are fed with performance goals in mind. Therefore, accurately assessing the level of work performed by a horse is essential in determining the amount and type of feed offered.

Energy is produced by aerobic or anaerobic metabolism. The breakdown of carbohydrates, fats, and protein into energy with the involvement of oxygen is termed an aerobic reaction.

Because oxygen is required, this energy-producing process is slow. The conversion of glucose or glycogen to lactic acid does not require oxygen and is therefore an anaerobic reaction, a process that produces energy quickly. Equine nutritionists divide work into three classes based on how horses derive energy from their bodies to fuel exercise.

High-intensity, short-duration work includes performance events with a primary sprint component