If we want to lift something, we need to have power in our muscles. If we want to run after a bus, our muscles need power to run. Even for the smallest movements we do, our muscles need to have power to do those movements. When the box we want to lift is heavy, we proportionally need more power to be able to lift it, and if we do less activity, our muscles need proportionally less power. But what exactly is this power that our muscles need?
When we want to move our bodies, we need to activate our muscles. This means our muscles need to create some kind of energy and force - which is called muscle power. In this post, I will talk about how muscle power is generated.
How is muscle power generated?
The power in our muscles comes from a molecular unit called ATP (Adenosine-Triphosphate). It is a combination of a nitrogen base, a ribose sugar and three bonded phosphate groups (C10H16N5O13P3). The bonds between the phosphates in ATP are of high energy, so when they are broken they create energy for our muscles to use.
There is a small amount of ATP always stored in our muscles. This ATP is used as a first source of energy for the muscles. However, this energy lasts only for a few seconds. After this stored ATP is used, new ATPs are produced by our muscles in two different ways -
- Anaerobic process - without using oxygen
- Aerobic process - using oxygen
Anaerobic Process
The anaerobic process of generating ATP is further divided into two sub-categories - first is by using Creatine Phosphate (CP) process and the second is by Anaerobic Glycolysis.
1. Creatine Phosphate (CP) Process: In this process, like the name suggests, Creatine Phosphate which is also stored in the muscle, is used to generate new ATPs. This process kicks in after the ATP stored in our muscles is exhausted. During CP process, the three phosphates in ATP are broken into ADP + P (ADP = Adenosine-Diphosphate, 'Di' meaning two in ancient Greek). For a new ATP to form again, a new Phosphate is necessary to combine with the left over ADP. This additional Phosphate needed to convert ADP to ATP is taken from Creatine Phosphate (CP), and a free Creatine is left over.
The number of ATPs that can be produced by this process are only a few. Therefore it can only last for a few more seconds. This type of energy can be used for short sprints or for some type of resistance training like weight lifting etc.
Once the ATPs from this process are also exhausted, the next process called Anaerobic Glycolysis takes over.
2. Anaerobic Glycolysis: Once both the stored ATPs, and the ATPs produced from the Creatine Phosphate process are exhausted, and if our muscles still don't have enough oxygen supply, our body will start breaking down carbohydrates into smaller compounds, called Pyruvates. These are then turned into new ATPs. Due to the absence of oxygen, this process produces only two ATPs from each Pyruvate. Anaerobic Glycolysis can keep our power supply without oxygen for about 90 seconds.
There is however one muscle protection process that kicks in during this type of ATP production, which is the build-up of lactic acid in the muscle. This lactic acid that is produced during anaerobic glycolysis prevents the muscles from overworking when there is not enough oxygen.
This type of energy is mostly used by our bodies during 200-400m runs, badminton, football/soccer, gymnastics, and other sports which need short bursts of energy lasting for less than 90 seconds.
Aerobic Process
This process to generate ATP works in the presence of enough oxygen for our muscles to use. This process of producing ATP is called Aerobic Glycolysis. During this process, the carbohydrates in our body are broken down into Glucose which is further broken down into elements called Pyruvate. Compared to 2 ATPs produced per each Pyruvate in the anaerobic/oxygen-free process, with the addition of oxygen, Aerobic Glycolysis can produce 30 ATP units per Pyruvate. This process is also called Citric Acid cycle or Krebs cycle. Apart from carbohydrates, this cycle can also use fats, and proteins to create ATPs.
ATPs produced by this process can be used for endurance exercises, like walking, long-distance runs, swims etc.
The following graph shows the energy generated over time for the three ATP generating processes - Creatine Phosphate Process (ATP - CP), Anaerobic Glycolysis (Glycolysis), and Aerobic Glycolysis (Oxidative).
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| Image Source: https://taekwondoanditsenergysystems.weebly.com/energy-systems.html |
In my upcoming blogs, I will share more details about how food is broken down to generate muscle power, and a detailed process of how ATP is used by our muscles.
Stay healthy and enjoy finding joy in health!