The Aerobic Energy System
We have three energy systems…
- Aerobic System (Sustain)
- Lactic System (Pain)
- ATP/PC System (Gain)
Throughout anything we do, from a 20 minute run to a heavy back squat we will use all three systems.
It just depends on the activity to which extent we use each one!
Today I will talk to you about the baseline energy system. The Aerobic System.
This system is our primary source of ATP.
ATP is Adenosine Triphosphate. This is our fuel.
All energy systems create it; how it is produced and the amount produced is what varies!
In order to create this fuel, the aerobic system primarily uses carbohydrates and fats.
When we are resting, about 70% of the ATP produced is derived from fats and around 30% from carbohydrates.
How Does It Work?
The aerobic system consists of three processes or ‘stages’ each of which produces ATP…
These stages involve more complex chemical reactions than the other energy systems which is why ATP production is much slower. (The more complex the process – the longer it takes to produce ATP)
The three stages which will be discussed in greater detail are:
1. Aerobic glycolysis (slow glycolysis)
2. Krebs cycle (also known as the citric acid cycle)
3. Electron transport chain
How Aerobic Glycolysis works…(the first stage)
- Initially, stored glycogen is converted to glucose. Glucose is then broken down by a series of enzymes.
- 2 ATP is used to fuel glycolysis and 4 are created so the body gains 2 ATP to use for muscular contraction.
- Pyruvate is created as the end product of the breakdown of glucose. As oxygen is present pyruvate is converted into a substance called ‘acetyl coenzyme A’.
- Acetyl-coenzyme A can then be synthesized in the second and third stages of the aerobic system to create more ATP.
Just for some physiological geography… the next two stages take place in the MITOCHONDRIA of our cells.
The Krebs Cycle… (the second stage)
Fatty acids (from fats) and amino acids (from proteins) are converted to acetyl coenzyme A, through a series of complex chemical reactions.
Along with the acetyl coenzyme A from glycolysis they enter the Krebs cycle and are broken down.
This results in ATP production and the by-products of carbon dioxide and hydrogen are produced.
The hydrogen produced in the Krebs cycle plus the hydrogen produced during glycolysis, left unchecked would cause cells to become too acidic.
Acidity in the muscle is what causes the anaerobic glycolytic system to fatigue.
So in the aerobic system hydrogen combines with two enzymes and is then transported to the electron transport chain.
Steps of the Krebs cycle:
- Acetyl-coenzyme A enters the Krebs cycle.
- Acetyl-Coenzyme A is broken down into carbon dioxide (a waste product which is expelled through breathing) and hydrogen.
- 2 more ATP is synthesised during this process and made available to fuel further muscle contractions.
- Hydrogen is transferred to the electron transport chain.
The main purpose of the Krebs cycle is to generate hydrogen to transfer to the electron transport chain where it can be ‘dealt to’ in a way that will control acidity and enable the aerobic system to keep synthesising ATP.
The Electron Transport Chain… (the third stage)
The electron transport chain is the most complex and productive pathway of the aerobic energy system.
Once in the electron transport chain, the hydrogen ions from the Krebs cycle undergo further chemical reactions.
Here they are combined with oxygen to form the end product of water.
The process of transferring hydrogen ions from its carrier molecules to oxygen and having the hydrogen ions move across a chemical gradient produces the energy required to combine ADP and Pi to form ATP.
In summary, the electron transport chain works as follows:
Steps of the Electron transport chain:
1. Hydrogen ions from the Krebs cycle are carried to the electron transport chain by carrier molecules.
2. Hydrogen ions are transferred to carrier molecules embedded in the electron transport chain where they go through a series of chemical reactions.
3. A hydrogen ion gradient is created. As hydrogen ions move across this gradient another form of ATPase phosphorylates ADP (adds another phosphate group) to form ATP.
4. Water is created as a by-product as hydrogen combines with oxygen.
But how long can I use this energy system for?
This energy system can produce ATP continuously for well over an hour. In fact, it may not have a limit as long as fuel sources can be found (you will die if this energy system cannot be used). However, your muscle glycogen will deplete after about an hour of exercise, which will result in an increased need for oxygen as fats become the dominant fuel source and use more oxygen per ATP produced than CHO.
Phew, now that’s over… what does it mean for me? How is it relevant to me? What does it actually mean?
So, we know how the energy system works. But for obvious practical reasons, we need to know what we can do with it, how we can develop it and how can we use it to get fitter, better and perform better all the time right?
When is it used?
So, the aerobic energy system is our baseline energy system. It is what is fuelling us at rest and in low-intensity activities. So, obviously for activities like a marathon, rowing or playing football, how well developed your aerobic system is, can play a big role in determining how well you perform in that activity.
Having a well developed aerobic system will allow you to maintain a higher level of intensity for longer periods when performing higher intensity activities. As it delays the effects of fatigue that may contribute to the deterioration of technical skill.
So for this – think workout classes – the better developed your pure aerobic system is – the better you can be at sustaining better form on an exercise. We all know the feeling when doing a ball slam for example and its the third round and you are shattered and your form goes to shit? Well.. spend some time developing this system and you can improve that!
Not only is it good for your ability during a session but also after. Aerobic fitness also involves int the ability to recover from high-intensity activities. Remember the blog about the grey zone and timing how long it takes for you go get back to it? Yep. This is this system.
How Do I Develop It?
There are two schools of thought here.
- You can develop this system with high-intensity interval type training
- You can develop this system with lower intensity, longer duration training.
Both are correct in that you can develop this system with both however it depends on so many variables which one is the best and also which one you may prefer.
So, if you remember the Blue and Green zone blogs, this is the zone we can be in but you can also develop it by being in the yellow and red zones.
Variables to think about:
- Your Initial Level
Your Initial Level
When the population is sedentary with a low initial level, the training program will produce a bigger improvement and the majority of exercises will be effective. So the lower the starting point the greater the improvement from any intervention.
Obviously, it depends on individuals and circumstances but for sedentary people, it should be 2-3 sessions per week.
This is the most important variable to manipulate and the one that creates the most opinions.
You can develop your aerobic system in two ways..
- with activities that allow you to stay in the blue and green zones. Your low-level work staying at around 60-75% max heart rate. So a longer row, or bike ride staying in these zones.
- You can develop this system with work and exercise with higher intensities so your red and yellow zones – 80-90% max heart rate
Now, for me, the best way to improve it for most people is using blue and green zones. And not because doing that activity develops it better but because it allows a better structure to your week if strength training (I think everyone should do some form of strength training so.…)
Because strength training is high stress on your systems and your nervous systems you need time to recover. If you did a session working on your aerobic system like a class where you have lots of red and yellow heart rate zones – this is another big hit on your systems and nervous systems causing more fatigue.
I would prefer a client or someone to use that day in-between strength sessions to do a green and blue zone day which has much much much less impact on your nervous system and fatigue allowing you to get your aerobic work in whilst not affecting your strength training.
Maximum gains seem to be obtained with sessions of 35-45 minutes.
I hope you found this blog useful and not too long!
If you have any questions about this energy system please come and find me and ask away!!