Muscle Exercise Energy Systems

Muscular movements are fuelled by three different energy systems. All exercises require different energy needs, many use a combination of the systems but often one energy system dominates in providing the energy for a particular activity.

The three energy systems handle separate demands depending on the degree of effort and endurance required. These energy systems work in sequence, a bit like switching gears.

All three energy systems produce adenosine triphosphate or ATP for short. ATP is the chemical compound in cells that give muscles the energy to walk, talk and lift weights.

Energy system # 1.  "ATP PC"

All cells store a limited amount of ATP ready for use. The amount of ATP stored between individuals often differs due to genetic factors and fitness levels. This system helps provide us with short bursts of energy lasting for about 10 seconds, however the higher the intensity the quicker these stores run out because more effort requires more energy. For example when performing a heavy set of Squats the stores may only last for 2-3 seconds. When ATP stores run out the cell switches to the next system to continue the production of ATP.

Energy system # 2.  "anaerobic glycolysis or Lactic acid"

This energy system is the most important for muscle building. Most weight training exercises predominantly use this system for energy production. It helps provide brief, intense energy for up to 3 minutes.

When exercise uses this system ATP is only partially broken down leaving a by-product of lactic acid. The build up of lactic acid interferes with further re-bonding of ATP molecules causing a burning feeling within muscles and resulting in muscle fatigue. Eventually the abundance of lactic acid causes the muscle to fail, thus one must rest briefly until the blood flushes out the lactic acid before this system can be used effectively again.

Energy system # 3.  "Endurance or aerobic system"

If an exercise is light the muscles still go through each energy system in turn but do not fatigue in the second system as there is no production of lactic acid. After about 3 minutes the muscles switch to the last system, the aerobic pathway.

Exercises that use this system are often performed at an easier pace and therefore tend to burn more fat. For this reason many people train this way to lose weight. The first two systems use predominantly carbohydrates for energy conversion and are used to develop more power, strength and muscle.

The time it takes for each person to shift into the aerobic pathway depends on various factors but physical fitness is a main factor. Also the fitter person can exercise at higher levels of intensity and still burn more fat, think about marathon runners who run hard, breathe heavy and they still remain very lean. Unconditioned or obese people tend to shift between the second and third system during most exercise. Due to the untrained muscles the cells find it hard to establish a regular and secure pathway.

 

Time factor	Energy system used
Up to 20 seconds	ATP PC stores in cells
20 seconds to 1.5 minutes	Combination of ATP & lactic acid systems
1.5 minutes to 3 minutes	Lactic acid system
Up to 10 minutes	Lactic acid & aerobic systems
After 10 minutes	Oxygen-based aerobic system

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