3 Ways the Body Produces Energy to Fuel Metabolism
ATP, which stands for adenosine triphosphate, is the sole source of energy for all human metabolism, yet very little of this fuel is actually stored in the body. Instead, the body has three different systems of ATP production: ATP-PC, anaerobic glycolysis, and aerobic phosphorylation.
Each system uses different starting fuels, each provides ATP at different rates, and each has its own downside (like fatigue). These differences mean that each method of energy production is best suited for particular kinds of activities.
The following table outlines the key characteristics of the body’s different ATP-producing methods.
|ATP-PC||Anaerobic Glycolysis||Aerobic (Oxidative) Phosphorylation|
|Description||Provides ATP at a very fast rate. Your body holds limited
stores of ATP-PC.
|Provides ATP fast, but not as fast as ATP-PC.||Provides ATP at a slower rate than the other systems, but is
great for endurance activities.
|Starting Fuel||Phosphocreatine (PC) stored in the sarcomere. PC combines
creatine and phosphate by using high-energy bonds.
|Glucose stored in the muscle and liver in a concentrated form
called glycogen. Glucose can be taken from muscle glycogen
or transported from the blood via the liver.
|Fats, carbohydrates, and proteins.|
|How Energy Is Produced||The chemical bonds that hold creatine and phosphate together
are broken, a process that releases energy that can remake new
|Enzymes in the cells convert glucose into lactic acid,
producing ATP. Although ATP is needed to get glucose into the cell,
you ultimately produce double the amount of ATP.
|Fats and carbohydrates are delivered to the mitochondria and
broken down to yield ATP. The waste product of a hydrogen ion
(H+) is bonded to oxygen to form water. The other waste
product is carbon dioxide (CO2), which can be breathed
|Amount of Energy Produced||Enough for about 10 seconds of very high-intensity exercise.
Total amount depends on stores of PC and enzymes to convert it to
|Enough to power heavy exercise for extended periods (2 minutes
or more). The amount depends on the availability of glucose and
enzymes needed for energy production, and the levels of lactic
|The amount depends on enzymes, the availability of oxygen to
the mitochondria, and the availability of carbohydrates and fats.
With training, high levels of intensity for very long periods of
time are possible (running a marathon at a 5 min/mile pace, for
|Used Most for Activities Like||100-meter sprint, short sprint, high jump, swinging a bat.||Intense activities lasting under 3 minutes, or during short
bouts of heavy work.
|Long-duration, low-to-moderate–intensity activities, like
walking, jogging running, hiking, and swimming.
|Cost or Tradeoff||When you run out of PC, you slow down or weaken.||Lactic acid builds up and causes the muscles to fatigue; it
also shuts down glycolysis.
|Work intensity is lower; running pace can’t be as fast as
a sprint. Altitude or another condition that limits available
oxygen (mountain climbing above 5,000 feet, for example) reduces
|How Training Maximizes these Fuel Sources||Increases stores and enzymes to make ATP faster.||Increases stores of glycogen and enzymes to make ATP faster and
to better neutralize lactic acid.
|Increases size and number of mitochondria and the number of
enzymes to make ATP.