Energy systems for the Mere Mortal

How many of us out there have heard of energy systems? If you are an active person, who might often geek out on the data and science of training then perhaps you have actually come across this graph above before or tuned into conversations that relate to the three/four/five different systems. I say three/four/five because depending on where you like to gorge on your science you will hear some systems be discussed in groups, others in specific scientific terms etc.

But I don't want to talk about the theoretical, not that it isn't important, but actually focus on the practical knowledge that we can take away and apply into our everyday mere mortal life.

Introducing our Mere Mortal and Energy

In all his glory, a mere mortal in the wild. Look at that physique and good fashion sense. Now you, me and everyone on this planet gets all of our energy from one place as humans.

Yes good ol sun, coming to the rescue and helping us out to continue living our wonderful life. Eventually the suns energy makes its way to us in the form of energy that we consume - food. The food we eat supplies the body with energy-rich molecules that once we finish breaking them down are what supports our body in running the various energy systems. In other words the conversion of our chemical energy to mechanical energy. Neat.

Practicality behind energy systems

So we get how energy comes into our system, but what's the point of knowing how it gets exerted and back 'out' of our system when it comes to being an active person?

Well - you are in luck that your body does this miraculous process all on its own as long as you are supplying it with the needful, otherwise your body would literally shut down, cease to function and die! Not a great outcome.

Understanding how energy systems work for mere mortals however has other practical benefits, namely that it gives us an ability to develop training plans at appropriate intensity and duration. Whether you are at the tippy top and are an Olympian, or merely want to perform better at your Saturday morning run, understanding how your body functions under various time domains can really give you a boost in the right direction.

A little bit of science

We can't escape understanding and grouping some of these energy systems in some form, so I have scoured the four corners of Google and tried to boil down the science into the most mere mortal explanation ever.


The system consists of adenosine triphosphate (ATP) and phosphocreatine (PC) interactions and is largely the system that operates in the first few seconds of your exercise, think an Olympic weightlifter. This is the dominant energy system in the first few seconds and drives your maximal efforts in a short time frame.

Anaerobic/Aerobic Glycolysis

A handful to say, but is simply the next set of energy systems that takes over after the ATP / PC system has done its thing by drawing on all those good carbohydrates (glycolysis) from your muscles for energy. The anaerobic/aerobic portion of this energy system delineates the different pathways that the chemical interactions take (lactate or acetyl-CoA as buzzwords to look up if you are interested). But simply its the energy an athlete might use in a 200/400m race with a trend towards a more aerobic system usage as the length of the action increases.

Aerobic Lipolysis

For when you need to go hours and hours, this system pulls the intramuscular triglyceride (fat) out, breaks it down into free fatty acids and glycerol (Lipolysis) to then create the energy required. Whether an ultra marathon runner doing 100 mile races or just going for large walks, the dominating system is this one for low intensity or lengthy activities.

Bringing them all together

Now that we have that level of understanding, let's round back and practically look at how this knowledge can be put to good use. The first thing is, these systems don't just switch on for a particular time domain of exercise before the next energy system turns on. Not at all. They co-exist in the wonderful dance that is energy production, providing a continuum ranging from rapid energy production all the way to slow energy production.

In saying that, each of energy systems has a particular domain of which it is king:

ATP / PC - 0 to 15 seconds worth of maximal effort is where you will find this energy system to be firing away. You will find this in actions like a max deadlift, Olympic lifting, sprinting, vertical/long jumps and other quick burst of movements. While a "full-throttle" system, it is highly unlikely most mere mortals will be able to sustain the output for more than those few seconds. Even trained athletes will require a few minutes (3-5+) of rest before they can perform the action at the same maximal effort levels. If you want to improve any movements that directly tap into this energy source, look to do maximum output actions with enough rest time to allow you to tap into the energy system fully again.

Anaerobic/Aerobic Glycolysis - Think 200 - 400m runs, or any activity that ranges from the 30 seconds to 10 minutes range. Largely a TON of activities fall under here, and you will know you are using this energy system when you feel out of breath after runs, when you feel that wonderful lactate flowing through your legs (that burning sensation one might get is the build-up of hydrogen ions) or undertaking some form of HIIT training. The glycolysis process also does incredibly well for fat loss due to its metabolic stress, so you will find better benefits trying to focus on the use of this energy system than say the ATP system for fat loss, if that is one of your goals.

The primary ways to improve or train this energy system is with repeated, high effort activities, normally avoiding a full recovery. Think a 200m run with 2:1 rest times or the usual bodybuilding style movements of sets of 12 with a minute or two rest in between. Enough that you can get your breath back, but just enough that there is a build up of effort and intensity to the activities.

Aerobic Lipolysis - The last in line, this energy system will become the dominant player in anything that starts to be counted in hours. Sports that will see this system be really used in stretches are field sports that might cross over that hour mark (soccer, basketball) or individual events like a marathon or cycling. To us mere mortals however, unless you are specifically looking to compete or excel at endurance events, then performing long and slow cardio sessions may not be the best or funnest way to enhance this system. As we spoke earlier all of these systems are in many ways interlinked, you are more than likely better off engaging in higher intensity training (true high intensity) that can develop your oxidative system and drive fat burning. Done right, you can actually see that after an intense training session a further window of time after training has ceased where your body will continue to burn additional fat! (EPOC if you want to go look into it further). So unless you are really looking to get specifically better at a long form activity, aim for high intensity training to help bolster this system as well.

The bottom line

In the end, I started writing about these energy systems in the hope that I could gain enough insight to suggest to other mere mortals how exactly you could focus in and improve based on energy systems. In part I feel like there is enough information there to advise someone, but ultimately I have landed on a bigger summarisation. As much as I want it to be all scientifically based, the reality is that unless you are pushing the elite boundaries, the real way to progress is less based on how do I best improve my mitochondrial respiration but rather, just do said activity more at a sustainable cadence that you can enjoy and improve over time. Leverage the above in partnership with known training routines to hone in where you want to improve, but ultimately have fun and ensuring regularity of activity will trump any infinitesimal small gain you might find in the precises science.

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