Energy Systems

When I first went into my work place, before I even had a job, my now boss said to me;
"If we use dollars and cents as our currency, what's the body's currency"? I had no idea! Well I'm pleased to say I do now!

The Body's Energy Currency is: Adenosine Triphosphate or ATP. ATP is used at the start of all exercise as there is not enough oxygen in the muscles.

Lets look at our Energy Pathways. Where do we get energy from?  We get our energy from food, but before we can use it, it must be broken down. ATP is needed for our cells to function and muscles to contract.

Carbohydrates, fats and protein are all nutrients that contribute to the fuel supply our bodies need to perform exercise.  These get converted to energy in the form of ATP. It is the energy that is released by the breakdown of ATP that allows our muscle cells to contract and our bodies to move. Each of these nutrients are made up of unique properties that will determine how they get converted into ATP.

Carbohydrates are the main source of fuel for moderate to high intensity exercise.
Fats fuel low intensity exercise and for long periods of time
Proteins are not normally used for muscle activity, but rather to maintain and repair the body's tissues.

ATP is not easily stored in our body and what is stored is used up within the first few seconds of starting exercise. As we continue to exercise we need to create more ATP. There are 2 ways the body converts nutrients into energy, they are:

1. Aerobic Metabolism, which requires Oxygen
2. Anaerobic Metabolism, doesn't require Oxygen

Anaerobic Metabolism can be further divided and often uses a combination of energy systems to supply our energy needs. Intensity and duration will determine which systems gets used and when.

ATP-CP
This system supplies about 10 seconds worth of energy during short bursts of exercise (Sprints, weight lifting). It first uses up the stored ATP in the muscle, which lasts for 2-3 seconds, then it requires creatine phosphate (CP) to make more ATP until CP runs out (6-8 seconds). The ATP-CP systems doesn't require oxygen to create ATP. After ATP and CP have been used up the body will move on to another energy pathway, either aerobic or anaerobic metabolism (glycolysis) to create move ATP to fuel exercise.

Limitations of this system:

• Only continue if fuel supply present
• ATP in muscles is limited
• Can only store 8-10 secs of ATP-CP
• Further regeneration of ATP comes from other systems

Anaerobic Metabolism (Glycolysis), Lactic Acid System
This pathway creates ATP from carbohydrates, of which lactic acid is the by product. It provides energy by the partial breakdown of glucose without using oxygen. The energy produced in this system is required for short, high intensity bursts of activity lasting only a few minutes, normally 1-3 minutes. The glucose comes from 2 sources:

• Blood glucose pool
• Liver and muscle glycogen (glycogen is stored glucose)

It is stored in the liver and muscles and in times of high intensity exercise glucose/glycogen is broken down and used for energy production. The break down of glucose required in this system give pyruvic acid, which in the absence of oxygen is further broken down into lactic acid. A build up of lactic acid (lactate threshold) will cause our muscles to stop contracting, muscle pain, fatigue and burning.

Aerobic Metabolism
This systems provides most of the energy needed for exercise of long duration. That is activities longer than 3 minutes. It is slower than the anaerobic system and requires the circulatory system to transport oxygen to the muscles to create ATP. It creates ATP from glucose, fats and protein. It supplies energy slowly and as it uses oxygen, carbohydrates and fats.


During exercise we will move through these energy pathways. The type of exercise will determine which system is used. As exercise begins we use the ATP that is stored within the muscles, once this is depleted we produces ATP via the anaerobic systems, as there is not enough oxygen in our muscles. Once there is an increase in our breathing and heart rate there is more oxygen available and we move into the aerobic metabolism system. We stay here until the lactate threshold is reached. Once here (lactate threshold) the body cannot deliver oxygen quickly enough to produce ATP and our anaerobic metabolism kicks in again. This is temporary and as lactic acid levels increase, our intensity decreases to help with the removal of lactic acid.


Ok.... Wow that is longer than I intended it to be. I'm going to leave it there otherwise you're not going to want to read it!!!

Joce