Anaerobic Energy System – Learn Body Reaction And Improve Performance

Learn the Anaerobic Energy System, body reaction to high intensity exercises

Anaerobic Energy System

There is much more happening within your body that you may never know.

As I keep dwelling into depths of the human body, I keep praising the almighty about how advanced and sophisticated technology works inside our own body, which is such a mystery, and science is still way too behind.

The energy systems are one such organized mechanism working inside our body that you may be mesmerized to know about as I unravel the mystery in most simple words.

I shall try to explain some scientific jargon as and when they appear so that you are not overwhelmed by the information provided here. 

Let me start by saying that if you are just starting in the fitness field or even if you are already an advanced athlete looking to improve performance, it is still beneficial to understand how our body energy system works.

It lets you implement the training in true spirit.

At the backend,  an engine drives every car, and the energy system is a significant part of that engine.

Let me first explain the meaning of the energy system before coming to the anaerobic energy system.

Energy System refers to the mechanism body adopts to provide energy as and when your body needs for day to day household works, walking, jogging, exercising.

There are two types of energy systems in broad terms.

1. Aerobic Energy Systems

2. Anaerobic Energy Systems

These systems are triggered together for fueling your activities, only the contributions of both energy systems keep varying depending upon the intensity of exercise.

You can assume them as gears of the car which body puts your energy systems in as the body starts increasing intensity of activity.

Let me explain to you with a brief introduction to both the energy systems before I move to our primary subject matter.


Aerobic Energy system

Aerobic Energy system produces energy only in the presence of oxygen to breakdown the carbohydrates, fat, and protein. As the aerobic energy system is out of the scope of this article, I would diverge from the main topic if I go in to complete details.

I shall keep touching this energy system time and again in the next few paragraphs to let you understand this system as well. So don’t get anxious.


Anaerobic Energy System 

Anaerobic Energy system works in the absence of oxygen by breaking down phosphocreatine, glucose and glycogen into usable energy. Unclear about terms just mentioned, wait, I shall come to this definition again.


Now you have an overview of both the energy systems and we can move to our energy system, which is our main point of discussion.

I shall try to dwell in too much more depth now without giving you an overdose of irritating super scientific jargon.

Let me now explain you anaerobic energy system in technical terms

As per NCBI ( National Center for Biotechnology Information),

Anaerobic energy system  is defined as the energy fueled by the energy sources within the contracting muscles during the physical activity of very short duration independent of use inhaled oxygen.

It means your body has the ability to produce energy and develop mechanical power even in the absence of oxygen by making use of resources available right inside the muscles to contract the muscles for the movement of the bones.

Clear enough! But you should not be. It is not that simple, nor is it that complicated.

I will let you understand the concept in the form of a few queries you might be coming up with to keep this topic interesting and engaging.


So, what kind of resources anaerobic energy system uses to produce energy without oxygen?

Answer  – There are three types of resources inside your muscles, which are readily available for immediate use.

1. Phosphocreatine

2. Glycogen

3. Glucose

However, these resources are not itself energy but need to be converted into a usable form of power when the need arises. The main advantage is the ability of these resources to convert into usable forms very quickly in the absence of oxygen.


So why do we need the anaerobic energy system in the first place?

We need an anaerobic energy system when you suddenly need a burst of energy all of a sudden.

The breaking down of food and converting them to more usable form such as carbohydrate, protein, fat through metabolism ( Visit this article  – What do you mean by metabolism? ) and turning them into energy in the presence of oxygen inhaled through lungs is a complicated and lengthy process.

So, when you suddenly start lifting heavy weight or do sprinting or grab a gas cylinder within a fraction of your brain signalling to do, it is not possible to provide energy that quick.

That is the situation where the anaerobic energy system comes in to play to assist you in coping with an initial burst of physical activity.

Depending upon the kind of resources used for providing energy by anaerobic energy system,

it is divided into two parts.

1. ATP-PC (Adenosine Triphosphate Phosphocreatine) Energy System

2. Anaerobic glycolysis or Lactic Acid Energy System.


But Why there are further two subdivisions of anaerobic Energy System?

There is a compelling reason. Both systems have their limitations. In case you are just starting HIIT exercise (High-Intensity Interval Training), the ATP-PC energy system can provide energy just up to 10 seconds within a moment.

Then the body needs to shift gear to Anaerobic Glycolysis provide energy for the next 3 to 4 minutes with immediate effect.

NOTE-  It is not that the Anaerobic Energy system works only after the ATP-PC system has done its job. 

As per semiprocycling,

Regardless of the type of effort, the body never closes off all the energy systems completely.

It means, by the time, ATP PC system stops delivering the Energy, Anaerobic Glycolysis becomes ready in 10 seconds to provide energy for the next 3 to 4 minutes in case of a trained athlete.

And after anaerobic glycolysis has exhausted its resources, the aerobic energy system comes in to play to provide energy for a much longer time then.



Let me now explain to you each subpart of the anaerobic energy system. Don’t stop here. It is essential to understand these sub mechanisms to help you know your body, develop patience, and listen to your body in a better way.


ATP-PC Energy System

The full form of ATP-PC is Adenosine Triphosphate – Phosphocreatine. It is that simple.

Let me explain to you both the biochemistry terms used in ATP-PC in the most comfortable manner.


Adenosine Triphosphate (ATP)

As per,

ATP is the primary energy currency not only in our cells but in all forms of life on the planet. All cells make it and use it to power their resources.

As above, ATP is the molecule in most preferred form muscle cells uses to produce energy in all living beings. That said, Everything we eat needs to be converted to ATP so that body organs may utilize to produce energy.

There is some fantastic biochemistry that happens behind ATP. But that shall be out of the scope of this article.

For the time being, just remember that ATP is the molecule, your muscles break down to produce energy in one single step.

Let us move to ATP- PC

As I explained earlier, PC refers to phosphocreatine, and this is the resource muscles use to convert to the molecule named ATP.

PC is always available inside muscle cells which convert readily into ATP in the super simple process as explained in this picture –


FACT – The simplicity of the process of ATP-PC makes it lightning fast in providing energy for the first 5 to 10 seconds without waiting for oxygen to arrive through blood capillaries inside muscle fibres.


Anaerobic Glycolysis

After you have vanished the primary energy system ATP-PC during the first 10 seconds of rigorous high-intensity workout, then comes the role of Anaerobic Glycolysis, which has already activated along with ATP-PC.


The process of anaerobic glycolysis explained


By the time ATP-PC energy pathway vanishes, body starts producing ATP by making use of resources named

1. Glycogen

2. Glucose

Glucose present within the muscle cells is referred glycogen, and glucose present in the bloodstreams inside the muscles is called glucose.

FACT – Glycogen, and glucose are present throughout the body in blood, liver, and all organs.

The only difference here is that in anaerobic glycolysis, glucose/glycogen is broken down in the absence of oxygen into the ATP.

Here are the steps your body adopts to convert resources of glycogen and glucose into ATP

  1. The First step your muscles takes is making use of glycogen present right inside the muscles to turn into ATP to provide energy for 1 or 2 minutes just after 10 seconds of ATP-PC.
  2. After glycogen has been consumed, present glucose right inside the bloodstream of muscles takes over for the next 1 to 2 minutes.

Interesting! Isn’t it.

And after, all anaerobic process has been exhausted, the aerobic energy system takes over finally.

I am sure that you must be mesmerized by the beauty of these energy systems. But before I finish this topic, there must be some more doubts arising in your mind like can I improve my energy system and increase ATP, what kind of exercise do i need to do improve my energy systems etc…

DO SUBSCRIBE AS I WILL UNRAVEL THOSE QUERIES in next few articles ( I apologize for not providing those details here as it shall make this discussion way more lengthier!).

I leave you with some fantastic insights into the anaerobic energy system you just read to take your understanding till this point to the next level.



Here we go to the most exciting part….


Have you heard about lactic acid and lactic acid threshold?

If you have been active in fitness for a long time, you must be aware of that. It is the by-product of anaerobic glycolysis as under

 Chemical formula for anaerobic glycolysis

As muscles start converting glycogen and glucose into ATP, lactic acid starts building up as a by-product. When lactic acid builds up to a level, you can no more maintain intensity, is called the lactate threshold.


Curious facts about Glycogen and Glucose resources

Each Glycogen molecule produces three no. of ATP molecules in the absence of oxygen, whereas a glucose molecule produces two no. of ATP molecules. That is the reason muscles employ glycogen before the glucose in the anaerobic glycolysis.

Glucose and Glycogen comparison in relevance to Adenosine Triphosphate


Volume of energy produced by Energy Systems (Comparison)

I don’t have the exact data available. Still, in broad terms, the energy produced in the ATP-PC  process is highest, and after that, energy production starts decreasing from anaerobic glycolysis of glycogen and then towards glucose. As such, the ability to maintain the intensity of exercise also starts falling from beginning towards the end of the anaerobic process.

Energy vs Time Chart of aerobic and anaerobic energy systems

FACT  – The rate at which our body make ATP during Anaerobic glycolysis is still 80 to 100 times faster than the rate at which anaerobic energy system can produce ATP from carbohydrate, fat, and protein.


Share this article with like-minded people to help near and dear ones.




Leave a Comment