Energy systems and how they work

Energy systems and how they work

We are going to fill you in on the different types of energy systems that keep our body working and how they act according to the level of physical activity that you participate in.

Types of energy

“Energy is defined as the capacity of a physical system to produce work”

Our body runs like a perfect machine, capable of adapting to the most extreme of situations, and for that reason is geared towards using this energy according to what is required in any given moment and what the physical activity consists of.

In this way, we can distinguish between two types of energy:

Potential energy

This refers to stored energy that is not being used but is available and could be accessed and used at some point. Through chemical reactions which involve the breaking of molecular bonds, a large quantity of energy is subsequently released.

Kinetic energy

Also known as available energy. This type of energy is active and in constant use while doing any kind of determined work. Synthesis is a process (work) that is carried out at cellular level, generating new molecules in the process.


When looking at exercise and physical training, it’s important to know which energy system is receiving ATP and having this knowledge allows for more efficient training.

What is ATP?

ATP stands for adenosine triphosphate, a molecule compounded by a nucleus (adenosine) and a group of three phosphates.

All living organisms use this substrate as a source of primary energy. ATP energy deposits are not particularly high, due to being constantly renewed and synthesised over and over.

Decomposition of ATP to produce energy is known as hydrolysis, as it requires water and results in a new molecule called ADP (Adenosine diphosphate)


ADP can change back to ATP (Phosphorylation) and as a result, be reused. This is known as the ATP/ADP cycle, a process which requires energy

ATP is constantly being recycled by the body, therefore constant energy support is needed for this continuous reaction to take place. When we do a physical activity, depending on intensity, the body demands a certain rhythm to avoid a delay in the energy supply.

In any case, when reaching higher levels of intensity and difficulty, said necessity becomes more noticeable. If our physical ability is limited, performance will be highly affected. If oxygen forms part of this process, what we have is aerobic metabolism, and without the presence of oxygen, this metabolism is considered anaerobic.

atp adp

The ATP-ADP cycle is linked to the storage and use of energy by living organisms.

The above information gives us a clue that the type of substrate will govern the speed at which the ATP can be recovered, in other words, the rhythm at which the energetic exchange is produced.

ATP and energy systems

The body needs energy to be able to work, whether this is in a seated position, walking or more intense physical work.

This energy comes in the form of ATP. The speed at which our body can make use of ATP is determined by three cardiovascular energy systems: in order to produce ATP, the body will deal with this demand based on both urgency and the quantity needed

Energy systems and how they work

Out of all of the physical challenges that a sportsperson inevitably has to face, the use of energy is one of the most significant

During the course of doing physical activity, there is a period in which our body changes from a basal state to an activation state. After this change, the body immediately begins a series of physiological processes-known as energy systems- that are fundamental for maintaining intensity and facing the imposed demand on the body.

These energy systems represent metabolic pathways used to transport and obtain energy for the body to be able to work.

As you have already seen, in all physical effort there is an intervention by the molecule fundamental to energy production, known as ATP (adenosine phosphate) ATP is generated upon the synthesis of foods by the three energy systems:

  1. Phosphagen system,
  2. Anaerobic glycolysis , y
  3. Anaerobic or oxidative system.

Energy systems

Result of using the energy systems

Alactic anaerobic system or phosphagen system

In this system, energy is obtained by capitalising on ATP reserves and Phosphocreatine reserves (PCr) found in muscle

For this reason alone, they represent the fastest source for getting energy and are used for explosive movements where there is no time for converting other combustibles into ATP.

The anaerobic system has two significant advantages:

  1. Lactic acid is not accumulated in the muscles
  2. Contributes a large amount of energy allowing for maximum intensity exercises, but only over a short amount of time. (no more than 8-10 seconds).

A good example of a training type that mostly makes use of this substrate would be HIIT. In reality, one of the ways we can boost our performance is through the use of supplements with creatine, and thanks to this supplement, we will be able to keep our ATP energy deposits at a high level.

Power clean

The efforts that are the most demanding and of short duration use this system

Another example of demanding physical activity which strongly involves this system would be a 1oo meters sprint or Olympic weightlifting

Lactic anaerobic system or anaerobic glycolysis

This system represents the principal source of energy in those sports which imply high intensity

When reserves of ATP y PCr run out, the muscle resynthesises ATP using glucose in a chemical reaction called glycolysis.

The anaerobic system provides sufficient energy to maintain the same level of intensity while exercising from a few seconds up to a minute.

The major limitation of this system is the forming of lactate, an acidosis which limits ability to perform exercise as a result of the muscle fatigue it causes.


That’s why the deployment of this mechanism is very important for athletes , due to their ability to adapt physically and develop a tolerance to this compound.

To counter this effect during physical exercise, substances that act as a buffer can be used to reduce this effect, as well as helping to improve the excretion of other metabolic residues derived from this process. anaerobic.

Among these substances we can find beta-alanina y citrulina malate

Aerobic and oxidative systems

When the glycogen reserves decrease, our body must make use of our oxidative system , in which our muscle uses oxygen, carbohydrates and fats as a chemical combustible

This system represents slowest method of getting ATP, however it can generate energy over the course of many hours resulting in its usage when a person wants to carry out a physical effort over a prolonged period of time.

Oxidative system

Considering the fact that this activity takes place over a long period of training time, the best option for improving recovery is through adequate hydration, giving the adequate minerals back to your body


To sum up, we have two energy systems that work without oxygen (anaerobic) and a system that requires a constant supply of oxygen (aerobic), which have very different levels of energy release.

These three energy sources stay active simultaneously at all times . That said, there is always a certain predominance of one over the other depending strictly on the type of activity that you are doing at any given time. Duration and intensity of the muscle contraction also play a big role.

This is the way in which each body uses a energy substrate , depending on the activity being carried out.

The ideal is to achieve metabolic flexibility, in order to use the distinct mechanisms that our body offers us in the most efficient way

Marathon runners know that the chances of finishing a 42 km race are directly linked to correct training and an excellent training routine.

Running half marathon

This allows for the most effective energy management and the ability to be prepared to use triglycerides as the main energy substrate

A 400m runner, on the other hand, will maintain a favourable balance towards the glycolytic pathway in order to finish the race giving their all, while a 100m sprint runner will make use of their system of phosphocreatines.

Related articles

Valuation of Energy Systems

Types of energy - 100%

What is ATP - 100%

Energy systems - 100%

Conclusions - 100%


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About Javier Colomer
Javier Colomer
"Knowledge Makes Stronger", Javier Colomer's motto, sets out his clearest statement of intentions expressing his knowledge and fitness experience.
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