Energy systems of human body

Our body is a ‘live machine’ which operates on energy we generate by the food we consume.

Most of the people think it’s all about ‘calories in’ and ‘calories out’.

We eat food- we digest it- it produces energy. As simple as that…!??? No, it’s not that simple. The middle part (digestion) is a huge multilevel process by the end of which we get the energy from the food. Let’s break it down further.

Our food does NOT directly convert into the energy.

We need energy for every type of movement whether it’s external (movement which are in our control i.e. moving body parts) or internal (movements which are not in our control i.e. pumping of blood by heart, circulation of blood, digestion etc.).

All the energy is comes from a molecule called ATP. Yes, it’s the most important and basic term in the world for energy systems. Every live animal on the planet need ATP to produce any amount of energy.

So what’s this ATP?

Adenosine tri phosphate (ATP) synthesized in our cells to produce energy. There are different ways our body uses to make ATP. It is called energy pathways. Our body don’t use same pathway to produce energy (ATP) for every type of tasks.

There are three pathways which are scientifically proven to produce energy in our body (Actually I believe there are lot more but these three are discovered till the date.)

1. ATP/CP Pathway.
2. Glycolytic pathway
3. Oxidative pathway

ATP/CP Pathway

This pathway is used when we go all out effort in very short time. For example movements like Olympic lifts, power lifting, shot put, etc. So this is anaerobic pathway. Which means oxygen is not used to produce energy.

Our cells stores ATP molecules for short term very high intensity movements. But this storage is very small so it only lasts for 2 to 3 seconds on the maximal efforts.

After that we have to wait to replenish our ATP stores.

Let’s breakdown this process. ATP releases energy when it’s broken down to ADP. Means three phosphate bond (tri) is broken down to two phosphate bond (di). When any type of bond breaks, energy releases.

Now this ADP cannot produce more energy so our body does a process where ADP again gets its phosphate back…! Yes, it converts ADP in ATP again. This is where CP (creatine phosphate) comes into action. It gives its phosphate to ADP and makes ATP again.  Now it’s capable of producing energy again. It is called replenishment of ATP. It takes 3 to 4 minute approximate for us to totally replenish ATP stores.

That’s why we need 3 to 4 minutes of rest to make second attempt of Olympic lift or power lift.

So how can one perform better at activities which uses ATP/CP pathway?

To know the answer of this question you have to understand some of the science of the muscle fiber types of human body.

There are two major types of muscle fibers.

1. Type -1 muscle fiber (slow twitch)
2. Type-2 muscle fiber (fast twitch)

There are two sub types of type -2 muscle fibers.

1. Type-2 A
2. Type-2 B

For now I will not go much deeper in this topic but what you need to know here is about type-2 B muscle fibers.

These muscle fibers are bigger in size and generally used in high intensity resistance training and explosive movements.

Means in all the activities of ATP/CP pathway our body uses type-2 B muscle fibers. Why?  Because they are bigger in size. So they can store more ATP molecules. However this reason is not confirmed yet by scientists.

So the bigger muscle you have the more better you can perform in ATP/CP pathway. Reverse is also true. The more you perform activity in ATP/CP path way the bigger muscle you will get. That’s the only reason Olympic lifters are so jacked.

Glycolytic pathway

If any activity lasts longer than 10 seconds Glycolytic pathway comes into play. Activities like 200 meter and 400 meter sprint, 50 meter swimming, high rep resistance training etc. are examples of Glycolytic pathway.

It’s just plan B our body uses to make ATP again after 8 to 10 seconds. Let’s dig little bit deeper.

When ATP/CP stores depletes completely our body uses glucose for anaerobic energy production. Which means this pathway also doesn’t use oxygen to produce energy.

Our body can use glycogen (stored in the muscle) or glucose (from the blood) to make ATP again from ADP. In this process waste product is lactic acid.

This lactic acid is the reason of burning when you do higher rep sets.

There are two processes which you need to understand.

1. Our body produces lactic acid as a waste product in process of breakdown of the glucose.
2. Our body can flush lactic acid out or It can make glucose again from lactic acid

Speed of process 2 is slower than the speed of process 1. However by practice and experience you can reduce the time difference between both processes.

Oxidative pathway

This is the pathway body uses for activities which last longer than 70 seconds. Long distance running like marathon, long distance swimming is examples of this type of activity.

This is aerobic pathway. Which means body uses oxygen to production of ATP. It’s done by the process called kerb cycle and electron transport chain. In this path way body produces more amount of ATP (energy) then other two pathways but it takes considerably more time.

In oxidative pathway body utilizes fat for energy production. No other pathway utilizes fat for energy production. However as intensity increases body starts using carbohydrates instead of fat. When carbohydrate (glucose) stores are completely depleted body starts catabolising muscle protein to produce energy. That is the main reason marathon runners are always skinny.

What general people should do?

If you are not an athlete you should focus on all round approach of fitness. Means we have to give equal time to all three pathways.

We should do activities for strength, endurance and long distance cardio. Divide your week equally with activities which uses all three pathways for better and overall fitness.

You can read my other article about overall fitness here. If you like this article you can share from below.

Source: ISSA (international sport science association)