[EN] Nutrients to muscle power (ATP)

The muscles in our body transform nutrients into muscle power units called ATP (Adenosine-Triphosphate), so they can be used for movement and daily activities. 

In my previous blogpost I shared how food we eat is transformed by our bodies into macro and micro nutrients. In this post, I share how these nutrients are transformed into ATP (muscle power). 

Nutrients to muscle power (ATP)

Even though the food we eat is transformed into macro and micro nutrients, the main sources of muscle power generation is only from the three types of macronutrients - Carbohydrates, Fats and Proteins. These three macro nutrients are further broken down into compounds during our digestive process:

  • Carbohydrates are broken down into Glucose
  • Fats are broken down into fatty acids, and glycerol. 
  • Proteins are broken down into amino acids
These compounds are used by the muscles to generate muscle power units called ATP. 

Glucose to ATP

The process where Glucose is used to produce ATP is called cellular respiration. This process takes place in the Cytoplasm and Mitochondria of muscle cells. This is a four step process:

Step 1 - Glucose to Pyruvate (Glycolysis)

  • In this step, Glucose is broken down into a component called Pyruvate. During this process 2 ATPs are produced for each Glucose molecule. 
  •  In addition to producing 2 Pyruvate and 2 ATPs, some energy is also passed on to energy carrier molecules (NADH) that will be used during a later state of this process to produce more ATPs. 
  • This process takes place in the Cytoplasm of the muscle cells. 

Step 2 - Pyruvate to Acetyl Coenzym A (Acetyl-CoA)

  • In the Mitochondria of the muscle cells, Pyruvate will be transformed into Acetyl-CoA.  
  • During this process, Carbon Dioxide is released and some energy is passed on to energy carrier molecules (NADH) that will be used during a later state of this process to produce more ATPs. 

Step 3 - Krebs Cycle (Citric Acid Cycle)

  • In this third step, called the Krebs Cycle, Acetyl Coenzym A (Acetyl-CoA) is transformed into two ATP molecules. As an intermediate step of this process, Citric Acid is produced, so this cycle is also referred to as Citric Acid cycle. 
  • Carbon Dioxide is produced as a byproduct and some energy is passed on to energy carrier molecules (NADH and FADH2) that will be used during a later state of this process to produce more ATPs. 
  • This process of Krebs Cycle takes place in the Mitochondria of muscle cells. 
Step 4 -  Oxidative Phosphorylation
  • In this last step, the energy captured in the energy carrier molecules (NADH and FADH2) is used to generate more ATPs. 
  • During this process, that takes place in the Mitochondria of the muscle cells, 32 ATPs are produced. 
  • As a byproduct, water is released. 
Image Source:  https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_
(Wakim_and_Grewal)/05%3A_Cells/5.09%3A_Cellular_Respiration

Fatty Acids and Glycerol to ATP

The fatty acids and glycerol produced from fats are used by the muscles to produce ATPs. This process takes place in the Cytoplasm and Mitochondria of muscle cells. This is also a four step process:

Step 1 - Synthesis of Glycerol and Fatty Acids

  • In this first step, Glycerol is broken down into a component called Pyruvate. These Pyruvate are fed into step 2 of the cellular respiration process described above for Glucose. 
  • Fatty acids from the fats are turned into Acetyl Coenzym A (Acetyl-CoA). These are fed directly into step 3 (Krebs Cycle) of the cellular respiration process described above for Glucose. 
Steps 2, 3, and 4 of this process are same as the cellular respiration process described above for Glucose. 

Amino Acids to ATP

The amino acids produced from proteins are used by the muscles to produce ATPs. This process also takes place in the Cytoplasm and Mitochondria of muscle cells. This is also a four step process:

Step 1 - Synthesis of Amino Acids

  • In this first step, Amino Acids are broken down into Pyruvate and Acetyl Coenzym A (Acetyl-CoA).
  • Pyruvate are fed into step 2 of the cellular respiration process described above for Glucose. 
  • Acetyl Coenzym A (Acetyl-CoA) is fed directly into step 3 (Krebs Cycle) of the cellular respiration process described above for Glucose. 
Steps 2, 3, and 4 of this process are same as the cellular respiration process described above for Glucose. 

Order of macronutrient selection

As there are three macronutrients - Carbohydrates, Fats, and Protein used to generate ATPs, there is a selection order that muscles use while generating ATPs. 
  • As the first option, our muscle use Glucose from carbohydrates to generate ATPs. This option is used first as the carbohydrate metabolism is faster compared to the fat metabolism. Protein is not used first as the amino acids are not readily available for ATP production.
  • The next option the muscles use is the fatty acids and glycerol from fats. Fat is the most concentrated source of energy, but the fat metabolism is a lot slower compared to the carbohydrate metabolism.
  • Proteins are rarely used for ATP production since amino acids (broken down protein) are not readily available in the body to be used for ATP production. Amino acids are used for ATP production only when our body no longer has access to other resources like glucose, fatty acids, and glycerol.

Having the knowledge of how nutrients are used in the context of our muscle power (ATP) can help us understand which foods support the activities we choose to do on a day to day basis. 

Stay healthy and fit and enjoy finding joy in health!