Description Of How The Body Produces The Energy It Needs For Exercise

To perform exercise continuously, the body requires large amounts of energy. The body often relies on carbohydrates -- using the adenosine triphosphate -phosphocreatine energy system, glycolysis and the aerobic energy system -- to provide sufficient energy. Additionally, fats and proteins can be used during beta-oxidation or gluconeogenesis to further provide the body with energy when carbohydrate stores are low.

ATP-Phosphocreatine

The fastest source of energy is the ATP-phosphocreatine system. During short, intense events such as a 100-meter sprint or lifting a heavy weight close to your one-rep maximum, the body must generate energy as rapidly as possible. To do so, it first relies on each cell's small amounts of ATP. When that supply quickly runs out, it uses the cells' supply of creatine to lend a phosphate molecule to adenosine diphosphate -- creating additional ATP to provide energy slightly longer.

Glycolysis

Because the ATP-phosphocreatine energy system has enough stored ATP and creatine to last no more than a few seconds, physical events that last slightly longer, including a 400-meter sprint, rely on glycolysis to provide energy. Glycolysis involves breaking down the muscles' glycogen supply into glucose, and converting that glucose into ATP. The "European Journal of Applied Physiology" in 2010 reported that those following a low-carbohydrate diet often have impaired athletic performance, as decreased glycogen levels that result from these diets cause a sharp drop in ATP able to be produced through glycolysis.

Aerobic Energy System

For lengthy physical events that can't rely solely on anaerobic energy systems, the aerobic energy system must aid in the body's energy production. During aerobic energy production, pyruvate molecules left over from glycolysis enter the Krebs cycle, which creates a compound known as acetyl coenzyme A or acetylCoA. This acetylCoA then undergoes the process of oxidative phosphorylation, which produces 34 ATP molecules. While this process yields more energy than the anaerobic systems, it is also less efficient and can only be used during lower-intensity activities, such as long-distance running.

Beta Oxidation/Gluconeogenesis

While carbohydrates are the body's preferred energy source, proteins and fats also provide energy. One way this can occur is through beta-oxidation, in which fats produce acetylCoA, which can then enter the aerobic energy system. Additionally, fats and proteins can undergo the process of gluconeogenesis, which converts these nutrients into glucose. While these are not the body's preferred energy-production methods, and they are significantly less efficient, alternative energy-production possibilities exist even when carbohydrate supplies are insufficient.