Energy Usage

While most people know that aerobic exercise is good for the heart and that resistance training helps build lean body mass, most people do not fully understand how these two types of exercise affect how the body utilizes fat, carbohydrate, and protein to produce energy.

In general, there are three basic energy systems:

• Phosphagen system (also known as immediate energy system).
• Glycolytic energy system (also known as nonoxidative or anaerobic system).
• Mitochondrial respiration (also known as the oxidative or aerobic system).

Regardless of which energy system is used, the end result is production of adenosine triphosphate (ATP). ATP is extracted from food we eat (fat, carbohydrate, and protein) and is required for biochemical reactions used in any muscle contraction. The intensity and duration of activity dictates which food types are broken down as well as which energy system predominates. However, no energy system acts alone. The relative contribution from each system depends on intensity and duration of activity.

The phosphagen system is active during all-out exercise that lasts about 5 to 10 seconds, such as a 100-meter dash, lifting a heavy weight, dashing up a flight of stairs, attacking with a flurry of techniques during sparring, or any other activity that involves a maximum, short burst of power. This system relies on stored ATP and to a larger extent, creatine phosphate, to provide immediate energy. For any maximal intensity exercise lasting longer than 10 seconds, assistance from other sources of energy is required.