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Understanding Energy Systems for Best Results

In order to get the most benefits from exercise we need to understand the different types of energy systems our bodies use when we exercise.


This is something we all should know when we are training for whatever goal we are chasing. We need to understand the energy systems our bodies use so we can know how to properly train. Each energy system differs in terms of energy source used, rest periods and intensity etc. So to gain the most benefit from your training, you need to understand the energy system that your body is using.

When we talk about our bodies producing energy specifically for exercise, we are talking about ATP (Adenosine Tri Phosphate). ATP is the energy rich molecule for all physical activity and it is present in our muscles, it is produced by glucose (carbs) mainly and also fat. When we use our muscles to exercise, we use ATP rapidly, so we need to restock, that's where energy pathways come into play.


The 2 main energy systems used are the aerobic system and the anaerobic system.

Aerobic - muscle fibres produce ATP in the presence of oxygen. This mean the aerobic system is used for activities that are prolonged and sustained such as long distance running or hiking.

Anaerobic - muscle fibres produce ATP without oxygen. Only happens when energy demand is greater than oxygen supply. This means the anaerobic system is used for activities that are high demand and quick bursts such as weightlifting or sprints.


Anaerobic system

This system does not rely on oxygen as it is for activities that are short interval or bursts such as weightlifting. This means that it uses the energy available in our muscle (ATP). ATP stored in our muscles are not stored in large amounts, that's why it needs to be quickly replenished. This is the reason why we can't lift weights for 30 minutes straight, our muscles run out of ATP, we need rest in between sets. Due to the small amount of ATP stored in our muscles, it is also quickly replenished. After 30 seconds, approximately 50% of ATP is restored, after 60 seconds, approximately 75% of ATP is restored. After 3 minutes, all ATP should be restored. This is why powerlifters and bodybuilders rest for a minimum of 3-5 minutes after a set, it is so their muscles can be fully replenished with ATP and they can lift with maximal effort again. It is the same with exercises like sprints as well, they are also under the anaerobic energy system. This system only uses glucose (carbs) as energy to produce the ATP as glucose provides more efficient energy quicker and glucose is also more readily available in muscles to quickly act and replenish ATP.


Aerobic system

This system is for prolonged activities such as marathon running. It uses oxygen to produce ATP from carbohydrates and fat. What we need to know is that we need oxygen to be able to burn fat. So this will come in handy for people who would like to lose a bit of body fat. When we start to exercise, our bodies will naturally go for glucose (carbs) first as energy due to glucose providing more efficient energy quicker. As stated in the Anaerobic system, ATP stored in our muscles are of limited amount, meaning that after around 3-5 mins of constant activity, our bodies start to struggle with replenishing the ATP. Our bodies will then automatically transition into the aerobic system. Our bodies will start to gather stored glucose in liver and blood along with fat to consistently produce ATP for our muscle cells. Since glucose stores are much more limited than fat stores, the more we go into aerobic exercise, the more our body turns to fat for energy.


FOR EXAMPLE - if we are 20 minutes into running, our bodies may be using 60% carbs and 40% fat as energy. But if we continue to run for another 30 mins (50 mins in total) then our bodies may be using 65% fat and 35% carbs as energy. These are just examples, not exact percentages of energy use.

The point is that the longer we go into exercise, the higher chance our bodies will turn to fat for energy as we have a much larger supply of fat than we do glucose.


To recap on what we have learnt, the anaerobic system uses ATP stored in muscles as energy. Short lasting and quickly replenished. Energy comes from glucose only. The aerobic system uses glucose and fat to produce more constant ATP for prolonged activity.

Now I want to finish off by saying that if you're going for fat loss, it doesn't mean you can't or shouldn't do exercises in the anaerobic system. Although the anaerobic system does not use fat as an energy source, the effects of the exercises in the anaerobic system may aid in fat loss. For example, weightlifting is an anaerobic activity, but if you increase your muscle mass due to weightlifting, it will increase your metabolism which may help you with weight loss. So it would be wise to add both types of training in your program.


I hope this information may be of use to you. Now you understand how each energy system works and the energy they use, may you all plan your routines accordingly.

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