Energy Systems: Who, What, When?


With summer around the corner and the likelihood that most peoples level of activity will sky rocket – I’m speaking from personal experience here of course. It is important to know what energy systems predominantly fuel your training and which ones you should invest the majority of your time in? What system has the most capacity for improvement and has a knock on effect of improving our lives?

The easy answer is – the aerobic system.

What are our three energy systems and which ones do what?

Two points of note as a foundation.

First, ATP – the cash in this money analogy is the energy our muscles use to contract during exercise.

Second, all energy systems kick in at the same time, it is not a staggered approach as I previously thought in high school.

  1. The Aerobic System (The Bill Gates Savings Account)

Think of this savings account as one that Bill Gates started for you before you were born and he put in a million dollars every year. Lets face it, you’ll never run out of money (energy). Of course, this is if you have a developed aerobic system – this system is the most adaptable and therefore you can return to it over and over for energy. This systems fuels life, from the energy needed by your brain to decide what clothes to wear in the morning to getting you through a tough training session.The aerobic system will improve your in the short term with consistent training. Unfortunately, it will also decrease after short periods of inactivity, usually a week.

The aerobic system utilizes oxygen for ATP (energy) production. This allows us to create long term energy.

A great way of training the aerobic system comes in the form of Cardiac Output or Steady State.

Now for the nerdy part. Cardiac output helps create an adaptation where the left ventricle of the heart works long enough that it stretches and gets bigger, therefore enabling a more efficient stroke volume (the more blood you can move in and out of the heart with each beat). Refer to “eccentric hypertrophy” in the diagram below. This is what happens to the left ventricle when you have a good chunk of aerobic based work in your program.

This expansion of the heart in turn makes your heart more efficient, lowers your resting heart rate and depending where your resting heart rate currently lies, can in fact flip a switch that allows you to start recovering properly and getting you closer to your fitness goals. I previously wrote an article on stress and how it impacts recovery here.

For this type of training you do not need to run tons of miles but getting on an airdyne bike for 30-40 minutes once a week or doing a circuit while keeping your heart rate in the 120-140 bpm will help you improve your resting heart rate, your ability to recover and deal with stress and also just make you feel good. As my friend Cosmo Kramer says, “Here’s to feeling good ALL the time”.


There are many ways to create a steady state session. An airdyne bike ride as mentioned above or you can create a circuit. Refer to my article “5 Reasons You Need High Performance Training” for an example of a high performance circuit I use for steady state work.


2. The Glycolytic System (Checking Account)

So I should state that this checking account is based upon being on a budget, it is not a bottomless pit – much like how I picture the savings account of Bill Gates referenced above.

The glycolytic or anaerobic system supplies energy for 60-90 seconds before it needs to replenish. It can generate ATP without using oxygen at a very fast rate. A side effect of the anaerobic system is that there is very rapid fatigue when it comes to mental and physical demands. Anaerobic training is draining and takes a lot of energy. Just think of trying to use the Tabata style conditioning for your conditioning every time you train. No bueno!

Compared to the aerobic system, over training of the glycolytic and alactic systems can cause thickening of the heart wall and increases heart rate as the stroke volume decreases. Refer to the graph above.


3. The Alactic System (ATP-CP System) (Credit Card)

The ATP-CP system provides energy for 10-12s. Like using your credit card, it should be used sparingly. Although there is a high power output there is also the least room for improvement and fatigue occurs quickly.

“Everyone has 8 seconds of free energy” – Charlie Francis

This system has the least amount of room for improvement. When used appropriately it can be a nice addition to meet your energy demands.

However, relying too much of the Alactic system can lead to some negative side effects. If you are constantly redlining during conditioning this means the glycolytic system and or the alactic system is predominantly in use and if you are unable to lower your heart rate quickly after bouts of high intensity exercise – your ability to recover is probably not optimal. This inability to recover is a result of a poorly developed aerobic system and an over utilized glycolytic system. Sub optimal recovery can lead to poor sleep, accelerated heart beat, failed fitness goals and just a general inability to relax.


In summary…

I like to think of conditioning in terms of the long game, the big picture – also known as life in general. The Pareto Principle should apply when it comes to conditioning. 20% of your efforts result in 80% of your results. The aerobic system is the system of life, but it also allows us to recover properly which in a lot of cases can be the missing piece when it comes to achieving your fitness goals.

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