In 1973, Secretariat ran the Kentucky Derby, a race of 1 1/4 miles, in 1:59 2/5, the fastest it has ever been run. Is this also an anaerobic event? Well, yes and no. Any event that lasts greater than one minute uses both anaerobic and aerobic metabolism to produce ATP. Aerobic metabolism is dependent on oxygen to break down fuel stores in the horse. Initially, there are limited amounts of oxygen reserves in the body that are present in myoglobin and hemoglobin. These molecules carry oxygen to the muscle and other tissues. However, these oxygen stores only last a few seconds to produce limited amounts of ATP. Inhaled oxygen during aerobic exercise is carried to the muscles and liver to metabolize carbohydrates and fats for the production of ATP. The end products of aerobic metabolism are carbon dioxide, water, and heat:

Aerobic metabolism is capable of producing 13 times more ATP than anaerobic metabolism because fat stores more energy than carbohydrates, and the end products of metabolism are not as toxic to the muscle. Horses using strictly aerobic metabolism usually have heart rates of less than 150 beats per minute during exercise, meaning the intensity of performance is moderate to low. Any event that lasts longer than 10 minutes at moderate to low intensities uses aerobic metabolism to produce ATP. Horses competing in the Pan-Am Endurance Championship ride will cover approximately 100 miles in 10 hours, a good example of aerobic metabolism.