Making Energy How our Bodies Work

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This article was edited and updated on November 18, 2019.

How do we get energy to do the things we do?

The simple answer is: We make it! It’s called ATP.

ATP (Adenosine Tri-Phosphate) is the energy we use to keep ourselves alive. They are manufactured within our body’s cells — and we need many of them every single second — for just about every imaginable task, including growth, movement, and metabolism. Oxygen and fuel (glucose or fat) are essentials for the manufacturing of them.

Simply put: More oxygen and fuel to the cells means more manufacturing of ATP which means more energy.

We can manufacture ATP in one of three ways and we use all three systems, depending on the body’s needs:

FIRST — The ATP/CP System: For Fast, quick energy

The body needs to have an immediate source of energy and the ATP/CP System delivers it. Creatine, a nitrogenous organic acid, occurs naturally in the body and helps to supply energy to our muscles. With the help of a special molecule, it produces ATP.

Our bodies have only a limited supply of Creatine, so this method of ATP production only lasts for up to 20 seconds.

It is used for short-term activities such as sprinting or in start/stop sports like hockey, rugby, soccer, or ultimate. It is important because it provides us with quick energy when needed.

SECOND — The Anaerobic Lactic Acid System: Using Glucose without Oxygen for Energy

Since the ATP/CP system lasts only for twenty seconds, we need another way to have energy that lasts longer.

The Anaerobic Lactic Acid System breaks down glucose and changes it into ATP without the use of oxygen (hence, the name anaerobic).

About 5% of the energy contained in the glucose is actually released, and several by-products are produced, including Lactic Acid, water, and carbon dioxide. This system produces less energy per molecule of glucose than the aerobic system.

At first glance, this system may seem inefficient and never preferable, but that is not the case. As with the quick-energy system, the Anaerobic Lactic Acid System is needed for our normal, day-to-day activities. It doesn’t burn fat, but ... it’s still very useful.

This system is a significant source of ATP when muscular activity continues for any length of time. It is often a natural bridge for energy production between the ATP/CP System and the Aerobic System.

The Aerobic System: Making Use of Oxygen and Fat Cells

In the first few minutes of any strenuous activity, energy must be made anaerobically. The Aerobic System comes into play when the amount of oxygen coming into the body is meeting the demand of the muscles.

As the heart and breathing rates increase, the demand for oxygen will be met and we create ATP aerobically. We will still be burning glucose, but much more ATP can be produced. Once oxygen is present in the muscle cells, fatty acid oxidation begins to take place, creating up to 100 ATP.

As the exercise carries on, we will begin to burn more fat instead of glucose. Since we cannot sustain intense exercise for long, it makes sense to exercise at a milder level for an extended period. As time goes by, the body will steadily burn more fat and less glycogen.

This efficient process occurs because fat as the main fuel has a much higher caloric density than glucose, allowing us to release far higher amounts of energy. Thus, stored body fat, combined with oxygen, becomes an excellent concentrated source of energy, generating ATP much more efficiently than glucose.

What does all this mean?

A summary of the major points of this article:

Note: Information for this article was taken from a course by Body Blueprint.

See also:

I am a BCRPA-certified fitness instructor in Vancouver, BC. I teach four classes at the West End Community Centre in Vancouver, BC, mostly designed for the older adult. The Inevitable Disclaimer: Everything published here expresses only my opinion, based on my training and research. What you do with the information is entirely your own responsibility. I am not liable for any injury you suffer that seems to be related to anything you read here. Always consult your doctor before beginning an exercise program. For other articles, return to the table of contents.

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