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Your body needs ATP, but how much do you already have in your body, and how does the process of creating more ATP work? Even though ATP is crucial, the body has only enough stored to perform a few seconds of maximal exercise.

For any maximal effort lasting longer than that, the body must regenerate ATP. There are a few systems in the body that can do this, each creating ATP at different rates and some kicking in depending on whether oxygen is available to the system or not. The three systems the body uses to transfer energy and regenerate ATP are:

•The ATP-PCr system (anaerobic)

•The glycolytic pathway (anaerobic)

•The oxidative phosphorylative pathway (aerobic)

To understand the three energy systems, imagine hiking up a steep grade. Suppose that you want to race your friends up it, so you begin to sprint. You feel fresh and have tons of energy. The energy you get for the first 8 to 12 seconds comes from the ATP-PCr system, which is anaerobic (without oxygen). It is the fastest available system you have. PCr is phosphocreatine, and when this bond is broken down by creatine kinase, the energy released is used to regenerate ATP.

Now you are moving fast on the steep terrain, but you slow down a little because your muscles start to burn. This burning means that your body is trying to find other sources of energy. This is when the glycolytic pathway takes over. This pathway actually kicked in at the same time as the ATP-PCr system did, but it takes a bit of time and is much slower to regenerate ATP. The glycolytic pathway uses glycogen stored in the muscles, takes glucose from the blood, and uses glycerol from triglycerides to regenerate ATP and keep you moving uphill. For ATP to be regenerated, 10 chemical reactions must take place. As a result, by-products are created: pyruvate and NAD+. At this point, if you keep climbing, there are two possibilities for regenerating more ATP.

KEY TERMS FOR ENERGY PRODUCTION

There’s no need to memorize these terms, but use this list to better understand the processes of energy production in the body.

Acetyl-CoA: A very important molecule that is involved in all reactions of energy production, such as the Krebs cycle.

Adenosine diphosphate (ADP): In order for ATP to provide energy for any given reaction, it has to split away one phosphate to release this energy, forming adenosine diphosphate (ADP). ATP can then be reformed when a free phosphate group is attached by spare energy and is stored again when it’s time to release a phosphate for another reaction. This recycling can occur indefinitely.

Adenosine triphosphate (ATP): This is the energy currency in all living cells. In humans it drives muscle contractions, nerve impulses, and just about any other reaction.

ATP-PCr system: This energy system provides immediate energy. Energy is released quickly and lasts up to 12 seconds in high-power movements such as bouldering or the beginning of any activity.

Beta-oxidation: The breakdown of fatty acids for energy use. We rely on this system to provide consistent energy during most endurance activities.

Creatine kinase: A critical enzyme used during the breakdown of phosphocreatine, splitting the phosphate group and using the energy released from this reaction to attach this phosphate to ADP for energy storage. This reaction is also reversible.

Electron transport chain: Found inside the mitochondria and used in tandem with the Krebs cycle, it is a “system” of rapidly moving electrons that creates kinetic energy that helps to regenerate ATP.

Gluconeogenesis: The formation of glucose from noncarbohydrate sources such as fats and proteins.

Glycogen: Units of glucose stored in body tissue.

Glycogenesis: The formation of glycogen from glucose.

Glycogenolysis: The breakdown of glycogen to glucose.

Glycolysis: The energy system that breaks down glucose to pyruvate that is eventually used to regenerate ATP.

Glycolytic pathway: Interchangeable term used for glycolysis.

Krebs cycle: One of two systems in the mitochondria that produces ATP during oxidative phosphorylation.

Mitochondria: Organelles found in cells that act as power factories, producing large amounts of ATP.

NAD+ and NADH: These are electron donors and acceptors. They are used to help move electrons through the electron transport chain to produce energy.

Oxaloacetate: A by-product of carbohydrate metabolism that can also be formed by gluconeogenesis. It’s an important intermediate for the Krebs cycle to produce ATP.

Oxidative phosphorylation: The aerobic energy system that produces the most ATP for endurance activities.

Phosphate (P): A substance used for energy in cells.

Phosphocreatines (PCr): A creatine molecule with phosphate groups attached to it that provides energy to form ATP.

Pyruvate: A molecule formed from the process of glycolysis and a key molecule that starts the process of the Krebs cycle. It can also be converted to lactate.

Triglycerides: An important energy source stored in fat cells formed from fatty acids. These can be released to use when energy is needed.

Research has shown that supplementation of creatine can help increase the availability of PCr, improve the amount of force your muscles produce, and improve power endurance, which is so important for difficult climbing objectives.