The 3 basic energy systems 

Fat adapted training is a totally different approach to energy utilisation, both for professional athletes and fitness enthusiasts. In this post, I wanted to talk a bit more about basic exercise energy systems. In fact, there are three different energy systems in which ATP (Adenosine triphosphate) production is possible. Different factors decide which of the systems will be running, and one of the decisive factors is the intensity of training. The ways in which our body can produce energy are:

1. Anaerobic – alactic energy system (ATP-CP System)

Phosphocreatine + ADP → Creatine + ATP

2. Anaerobic – Lactic Energy System

Glucose → Lactic acid + ATP

3a. Aerobic Energy System (= aerobic glycolysis, oxidative degradation of glycogen)

Glucose + Oxygen → Carbon Dioxide + Water + ATP

3b. Aerobic Energy System (= lipolysis, oxidative degradation of fats)

Fats + Oxygen → Carbon Dioxide + Water + ATP

Anaerobic alactic energy system (ATP-CP system)

The anaerobic alactic energy system or creatine phosphate system gives us energy from the start.  For example, the first three or four reps or, maybe, when you are starting a sprint. So, during the first 5 seconds of exercise, regardless of the intensity, the ATP-CP system is used exclusively.

The anaerobic lactic energy system

Now, the anaerobic lactic energy system which is second in row utilises carbohydrates*. This system provides us with energy from 5 up to 15 maybe 20 reps. On the contrary, the aerobic system is activated mostly during low or middle-intensity exercises. It is called aerobic because it needs oxygen to operate and produce ATP. When we are following the ketogenic diet, it’s important to understand that we don’t have a whole range of energy systems. What does this mean?

*In the anaerobic lactic energy system, the presence of carbohydrates is essential, which means that we don’t qualify to operate that pathway properly regardless of our Fat adapted state. However, there is plenty of energy from the anaerobic alactic energy system available to us.

Aerobic energy system

So, during the physical activity, all these 3 energy systems are supplying the body with the necessary energy. Of course, none of the systems can work independently but rather dominate at different times. It always depends on the conditions of our performance.

Humans have evolved through aerobic activities, and for that reason, it’s not a surprise that the aerobic system, which is dependent on oxygen as the name says, is the most complex of all three energy systems. Metabolic reactions taking place in the presence of oxygen, but the aerobic energy system is the slowest way to reshape ATP.

Old vs. New 

In the past, there was a perception that the involvement of energy systems in the production of muscle energy was done in the same time sequence. Today, however, we know that this is not the case. We accept that all energy mechanisms participate simultaneously in the production of muscle energy. Of course, with the relative contribution of each mechanism depending on the intensity, duration and evolutionary stage of the exercise.

Oxygen supply plays a key role

Generally, we could say that in an effort of short duration and high intensity the anaerobic mechanism prevails. On the other side, in the long-term efforts of low intensity, the aerobic mechanism of energy production is dominant. Although we do not know exactly how this energy regulation works, oxygen supply seems to play a key role.

Since the energy needs of an exercise are met by different mechanisms, in order to study the contribution of each mechanism, we have defined three phases of energy expenditure delineated by oxygen intake. At different stages of development and depending on the intensity we recognise these three phases:

1. Transition phase

2. Stabilisation phase

3. Rehabilitation phase

The three phases based on the oxygen-derived delimitation are shown in the diagram below.Fat adopted Based on this diagram, we note that before the exercise the oxygen intake is stable and low. However, once the exercise begins, the body’s energy needs are greater than the energy it can produce using the available oxygen. This is mainly for two reasons:

  1. The cardiopulmonary adjustments which are required to increase the supply of oxygen to the tissues are taking more time
  2. The generation of aerobic energy is slow compared to anaerobic systems

Stabilisation phase & transition phase

Next, as shown in the diagram above, the oxygen uptake stabilises and this phase is called the stabilisation phase. This phase follows the transition phase after a few minutes with the time decreasing as the athlete’s effort increases. When the exercise is relatively mild, then the energy demands are met by oxygen intake. The athlete can continue to exercise for a fairly long period of time.

This, of course, does not occur when the intensity of exercise is high. In this case, the stabilisation phase is apparent since even the maximum oxygen uptake is not enough to meet the energy requirements. The anaerobic mechanisms continue to cover the resulting energy gap. Naturally, this leads to the depletion of energy reserves and the high concentration of lactic acid, resulting in tiredness. At this point, the exercise will stop in just a few minutes. The above is also shown in the diagram below:Fat adaptedNow, during the recovery phase, oxygen uptake remains elevated over a period of time, the duration of which depends on the intensity of the exercise that preceded it. The higher the intensity, the longer the rehabilitation will be. The oxygen consumed during this phase is used to restore body functions to rest.

Fat adapted state

Fat adaptation of the metabolic system shook the world of many athletes and trainers. Imagine, from a dominant fuel source of glucose to a principal fuel source of fat. This might come as a surprise to carb-eaters, but Fat adapted state is the preferred metabolic status of the human organism. Before the food pyramid created the obesity epidemic, people were in a constant annual circle of fat adaption, based on circumstances such as area, weather, season and food rations.

Fat adapted life

Fat adapted state means you can efficiently burn deposited fat for energy during the day. Even the slimmest person who scales 60kg with 9% of body fat has 6 kg of fat, which at 9 calories per gram is 54,000 calories for potential usage. For athletes, fat adapted state also means you can depend on your own fat for energy through your athletic activity. This gives a glycogen saving result, so this carbohydrate stored in the muscle is free to carry the large intensity activity (or wherever it is most needed).

Very well trained athletes

Even if you are a professional athlete with 2000 calories of muscle glycogen storage, if you are a sugar-burner, that spends 1000 calories/h, you will certainly run out of energy after 2 hours. There’s always some 700 calories missing. On the other hand, as a fat adapted athlete, you’ll be covered for hours!