Our Energy Systems

Did you know the body relies on three energy systems, dependent on the intensity of any given activity?

Lets take a little look at how it all works:

So, we know that we need to eat food for energy in order to move, stay warm and stay alive, but how do we use them? Muscles need energy in order to contract and create movement. Sometimes they work at low intensity and need a slow steady supply of energy, where as other times the same muscles  work at high intensity and must work with maximum speed and power, so stores of explosive energy have to be available instantly. Just like a car has gears the body has three different systems of energy depending on the intensity of what we ask it to do.

These energy systems are:

* Aerobic.
* Lactic acid (Anaerobic Glycolysis).
* Creatine Phosphate (Anaerobic).

Before looking at each energy system in more detail, we need understand the fundamental concepts of energy production. A quick overview of Macronutrients (Carbohydrates, Fat and Protein) reminds us that carbohydrates contain 4kcal/g, protein contains 4 Kcal/g and fat contains 9 Kcal/g. Through digesting these macronutrients and breaking them down, we acquire our energy.

The Aerobic Energy System.

Let’s have a little look at the aerobic energy system. If you’re doing something that isn’t really hard work, like taking a walk with the dog, or taking the kids to the park, your muscles move to let you do it.

What happens inside is quite interesting! In a simplified way, the sugar from your food (glycogen) mixes with the oxygen you breath in. A chemical reaction happens inside your muscle and energy is released in the form of movement.

Now because the intensity is low, your body can do this over and over again, provided you give it enough glycogen and oxygen, and you won’t feel too troubled. Simple right? Have you ever heard of the fat burning zone? This is part of the aerobic energy system, and requires a low intensity exercise, such as walking or slow jogging in order to work.

When you give your body lots of time to get the glycogen to make its energy, it can break down stored fat and use it for fuel. Next time you’re on the treadmill, bike or cross trainer at the gym, have a look at the chart and you will see ‘fat burning zone’ right at the bottom of the intensity chart.

If you work a little harder, your body won’t have time to break down the fat, so it has to get your energy in another way. Enter carbohydrates. These can be converted much quicker than fat, so we need to make sure we eat them when doing a higher intensity of exercise.

Your body, being the wonderful product of evolution that it is, will adapt to these new demands and become more efficient at making this energy available for you to use, so the more you train in the aerobic zone, the more stamina you will gain.


The Lactic Acid Energy System.

The lactic acid (Anaerobic Glycolysis) energy system is one we should all know very well! This is the one that gives you the burning feeling when you are performing a high intensity exercise, but, why does it burn?

Firstly, lets look at how it works. Remember the aerobic system using oxygen – this one doesn’t. With the lactic acid system, there isn’t enough time for the body to do all of the reactions with oxygen to make your energy, so it cheats.

It breaks the glycogen down partially, some is used for energy and some is kept behind because the oxygen isn’t there to help complete the reaction. It’s the leftovers that burn. So, in effect, all you’ve really done is borrowed this energy for a while, and afterwards you will need to pay it back.

Once the high intensity exercise is completed, and all the waste is left behind, your body will use oxygen to neutralise it, and go back to the aerobic system once it’s all gone. In simple terms, it’s an oxygen debt that you need to repay, which is why you breathe harder after intense exercise.


The Creatine Phosphate Energy System.

Lastly, we have Creatine Phosphate. This is similar to lactic acid in a way, because it also doesn’t require oxygen to work. If you think about what activities you do most of the time, you’ll see that they don’t require lots of high intensity effort. Our bodies know this, so they’re focused on providing sustained energy. On occasions though, you need to use maximum effort.

Maybe you need to run after your dog on the park before it escapes, or you’re lifting a really heavy weight to increase your strength. In these instances, we use our Creatine. We only have a little supply of this in our bodies, because we don’t run around at 100% all of the time, so we are limited with the time we can operate at this level.

Most normal people have around five seconds worth of Creatine available to use at full intensity, but did you know that someone like an Olympic athlete can store much much more? As with all forms of exercise and training, we can make our body learn and adapt so it can get better at doing the things we want it to do, so it is important to know the basics of each energy system to get the most out of your training program.

A quick example would be resting times. If you’re in the low intensity aerobic zone, you won’t need much rest time because the body can keep using oxygen and glycogen to make its energy. If you’re in the lactic acid zone, you need to repay the oxygen debt after a while, so you’ll need to rest in between sets or intervals.

Lastly, if you’re in the creatine phosphate zone, you’ll need to allow even more rest for your body to resupply the little creatine stores you’ve just used up. When you rest properly depending on what energy system you’re using, you will be able to perform at your optimum level for longer, and make the most out of your time whilst working out.


In Summary.

What does this all boil down to in the end? Well, if we think about it logically, it all points towards nutrition. We need the right nutrition to compliment our training and it has to match the demands of the energy systems we use most often.

If you spend a lot of time working in the aerobic zone then you will want lots of slow release energy, which comes from your complex starchy carbohydrates, like potatoes, pasta and rice. If you’re working in the creatine zone, then supplements such as creatine powders can help to boost your training.

Our body is just a vessel where chemical reactions take place, so sticking to the fundamental principles of the energy systems and nutritional requirements will ensure consistent and reliable results that enable you to reach your goals.

In order to achieve a healthy, balanced fitness level, it is essential to use all three of these systems in a well structured exercise program. During these training programs, you will have rest periods to allow your muscles to refill their energy stores.

Sometimes you might notice people in the gym resting for longer than others – this is because each energy system has a different timescale for replenishing spent energy. The aerobic system can operate for a long time and needs little rest because the body has time to keep creating its energy.

The anaerobic system requires a higher period of rest in between sets or intervals in order to repay the oxygen debt and get rid of the lactic acid build up from the higher demands placed upon it. The creatine phosphate system requires the longest amount of rest time because it takes the longest time to replenish the muscle cells.

This can be between 3-5 minutes of rest to make sure they’re fully topped up again and ready to perform at the optimum level. If you want to know more about the energy systems in detail, such as the processes involved in making our energy, and how the muscles use it, be sure to check back for some of our more in depth articles which go into greater, more scientific details. Until then, keep pushing, and keep training.


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