The muscular activity produced during a race comes from both aerobic and anaerobic metabolism. Some people have thought that the Quarter Horse uses mostly anaerobic metabolism for the energy of a race, but recent studies in equine exercise physiology have shown that most energy used in even a short race comes from aerobic metabolism. The splitting of glycogen molecules to obtain energy results in the by-product lactic acid. Oxygen combines with lactic acid to produce carbon dioxide which is eliminated during respiration. During intense activity, however, there is not enough oxygen to neutralize all the lactic acid and it builds up in the muscles interfering with their function.
Heat build up during intense exercise also interferes with maximum muscle function.
Many substances interact in this whole process to make it work more efficiently. The ergogenic aids act in some aspect of this metabolic process of converting fuel to muscular energy. One researcher described ergongenic aids as substances that function in one of four ways. They may act as a supplementary fuel source for energy production. They may affect the flux of fuels through the energy pathways.