dbal lean muscle

Exposing the 3 Energy Systems in the Body

If you’ve already seen our previous article, where we discussed the “Training parameters”, you must know that the different ratios of intensity, volume and density, activate different energy systems in the human body.

Different energy systems activated, means different end results achieved.

So, if you still haven’t seen that article, we highly recommend you to do so, by clicking HERE.

Reading and acknowledging that information will help you make sense out of things easier.

Now in today’s article we will discuss these energy systems, as well as some of their elements, to help you understand them.

The 3 systems

As we know, every movement of every living being here on earth, requires a certain type of energy to be released.

“Muscle contraction and, therefore, all exercise are dependent on the breakdown of adenosine triphosphate (ATP) and the concomitant release of free energy (1). This free energy release is coupled to the energy requirements of cell work, of which muscle contraction is just one example” Says the US National library of medicine1

In the human body, there are 3 main energy systems-

  1.  Anaerobic-A-Lactic
  2.  Anaerobic-Lactic
  3.  Aerobic

These may sound a bit complex, even though you’ve probably heard the last one, so let us break them down for you and help you make sense out of their names, before we define each one individually.

Reference terms

  • Aerobic and anaerobic processes
  • Lactic acid
  • Adenosine triphosphate (ATP) & adenosine diphosphate (ADP)
  • Creatine phosphate
  • Glycogen

Anaerobic Energy System

Aerobic and anaerobic processes

Granted, these articles will educate you, using layman terms. So, let’s start by understanding what the aerobic and anaerobic processes are.

Aerobic processes are essentially energy-releasing processes, that require oxygen. Simply put- Aerobic means “Requires oxygen to release energy”.

However, we also have the anaerobic energy releasing processes, which do not require oxygen to release energy, so, anaerobic means “Does not require oxygen to release energy”.

Simple as that.

“The anaerobic (nonmitochondrial) system is capable of responding immediately to the energy demands of exercise and is able to support extremely high muscle force application and power outputs.” US National library of medicine2

But what does alactic/lactic mean..?

Lactic acid

This is basically a byproduct of intense muscular activity. Lactic acid builds up in the muscle, the more we use it.

What lactic acid does is it basically speeds up the exhaustion and fatigue of the working musculature.

Generally, the more developed a muscle is, the easier it will recover from the lactic acid build-up.

The more blood is flushed through it, the quicker the lactic acid will be flushed and hence, the energetic structures will also be recovered.

That is to say that a more developed muscle will get exhausted more slowly and will recover quicker.

So, knowing these two reference terms, we can conclude that “Anaerobic-A-lactic” would translate to “Doesn’t require oxygen to release energy (Anaerobic) and DOESN’T lead to a build-up of lactic acid (A-Lactic)”.

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Adenosine triphosphate (ATP) & Adenosine diphosphate (ADP)

As we mention, every single movement of every living creature on earth, requires energy.

For ALL living creatures, that energy is stored as ATP, including the energy inside of human muscle tissues.

ATP is produced by all 3 energy systems in the body and during intense muscular activity, it momentarily grants a big amount of energy.

Once used up, ATP breaks down to adenosine diphosphate- ADP.

Even though ATP grants energy momentarily, its storage is limited and hence, it grants energy for short periods of time.

This is where the next term comes into play- Creatine phosphate

Creatine phosphate (CP)

Creatine phosphateCP is a compound in the body, made out of creatine and phosphoric acid. CP in the body, serves as an energetic reserve, within the tissues.

When ATP gets used up and breaks down to ADP, the body combines ADP and CP to regenerate the ATP, which only then grants the muscle energy for some more time.

Last but not least-


Glycogen is basically a complex carbohydrate, which is essentially the main fuel source for the body.

It is the end product of carbohydrate metabolism and is stored inside the muscles but is also secondarily stored in the liver.

During strength training, the body uses the muscle glycogen, which is also another reason why it is best to do your cardio after a workout.

Knowing this, we can say that low-carb diets are a literal body-burnout for people trying to lose weight and do resistance training at the same time and high carb diets are man’s best friend when it comes to building quality muscle tissue.

Now knowing these, we can move on to explaining the 3 energy systems:

  • Anaerobic-A-lactic energy system


This is the single most powerful energy system in the human body.

It does not require oxygen to function (Anaerobic) and it does not result in a build-up of lactic acid (A-Lactic).

Its main sources of fuel are the ATP and CP reserves inside the muscle tissues.

This energy system is the quickest to recover ATP, but can only do so for short periods of time.

The ATP reserves last for the first 5 seconds of work and then, once the CP is also used up, we have another 10-20 seconds.

So, we can say that the body uses the Anaerobic-A-Lactic system to overcome high-intensity workloads that are short in duration (5-25 seconds), such as a 100- or 200-meter sprint.

  • Anaerobic-Lactic energy system

This is the second most powerful energy system in the body.

Again, it does not require oxygen to function (Anaerobic), but unlike the first one, it leads to a build-up of lactic acid, due to the breakdown of glycogen, hence its name.

The anaerobic-lactic acid uses muscle and liver glycogen to recover ATP.

This is the second quickest system to recover ATP, but again, it does so for relatively short periods of time.

Our bodies use the anaerobic-lactic energy system to overcome moderate to high-intensity physical activities, that last for up to 2 minutes.

As an example here, we can take the 400m sprint.

“It is well know that both anaerobic pathways — lactic and alactic – are activated instantaneously at the onset of maximal activity. Billat, L. V. (2001). Interval training for performance: A scientific and empirical practice.3

Last but not least…

  • Aerobic energy system

Aerobic Yoga EnergyThis last energy system is the least powerful of all 3.

The aerobic system, as you can guess by its name, requires oxygen in order to release energy.

As a fuel source, the aerobic energy system uses liver glycogen and fats, as well as proteins if the first 2 are not available.

This last energy system is the slowest one to recover ATP, BUT it is the most sustainable one, as it can do so over long periods of time.

Our bodies use this energy system to overcome low-intensity physical activities, that are long in duration- More than 2-3 minutes.

A good example here would be a 5000 meter cross-run.

When one does aerobics first and then high intensity training the workout is sub-optimized in all aspects. University of Michigan Medical school4


So, what we basically learned today is that ATP is required for every single movement of every living creature.

It is the purest source of biological energy, and during very intense physical activity, it grants energy, momentarily.

However, its sources are limited, and even though CP recovers it, it lasts for short periods of time.

As muscular activity is prolonged, the body starts utilizing the muscle glycogen, which also leads to a build-up of lactic acid.

If our activity is prolonged, more than 2-3 minutes, the body starts using the liver glycogen to release energy.

Now each of these energy-releasing processes leads to a different outcome, so make sure to check out our next article, where we discuss a very commonly asked question: How does the muscle grow?

See you there!

Products Guides:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3005844/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3005844/
3. https://coachsci.sdsu.edu/csa/vol71/billat3.htm
4. http://umich.edu/~medfit/resistancetraining/timingiseverything101705.html

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