Muscles are made of amino acids | Functions and breakdown mechanisms of BCAAs and essential amino acids

[Digest video] Learn the basics of "muscles" that are essential for building a healthy body through illustrations

Muscles are made up of amino acids – essential amino acids and BCAAs (branched-chain amino acids)

What is the relationship between our bodies and amino acids? Do you know what the human body is made of?

Components that make up the body – water and protein

As shown in Figure 1, 60% of our bodies are made up of water, 20% are proteins, and the remaining 20% ​​are lipids, carbohydrates, minerals, etc. If you exclude water, which makes up 60% of the total, the remaining half is protein. This protein is made up of just 20 types of amino acids bonded together. In other words, "half of the human body is made up of amino acids."

Muscles, which are important for exercise, are also made up mainly of protein. These 20 types of amino acids are divided into essential amino acids, which cannot be produced in the body and must be taken in through food, and non-essential amino acids, which can be produced in the body. Among the essential amino acids, muscles contain a lot of BCAAs (branched-chain amino acids), which are well known to athletes, and it is said that they account for about 40% of the essential amino acids contained in muscles.

Muscle fiber growth through strength training

Muscle training is essential to improving athletic ability. When you train your muscles, they become thicker and stronger. If you look closely at muscles under a microscope, you will see that they are bundles of long, thin cells called muscle fibers. When you train, your muscles get bigger, mainly because each muscle fiber gets thicker.

Figure 1

Muscle and Amino Acid Replacement | Daily Protein Intake is Important

We don't feel it, but in fact, new proteins in the body are constantly being produced and old ones are constantly being broken down, that is, replaced. As shown in Figure 2, for an average adult weighing 60 kg, about 1 g of protein becomes old and is broken down each day. And the same amount of protein is newly produced.¹⁾This balance is maintained by consuming the daily required amount of protein, so it is important to get enough of it from your diet.

Figure 2

When you eat protein, it is broken down into amino acids, absorbed into the body, and distributed throughout the body via the blood. These amino acids are then used to make proteins in various parts of the body every day. You probably don't realize it, but a certain amount of protein (amino acids) is released from your body every day. In other words, to maintain the balance of protein in your body, you need to take in the same amount of protein every day as is released. The same is true for muscles, where the protein contained in them is replaced little by little every day, and it is said that half of it is replaced over the course of about six months. In other words, muscles are completely replaced in just about one year.

Protein intake requirements for athletes

Recent American College of Sports Medicine (ACSM)²⁾Announcements by the International Olympic Committee³⁾Therefore, athletes are recommended to consume 1-1.2g of protein per kg of body weight per day (2.0-60g per day for a 1kg person). The average protein intake for an adult is 72-120g per kg of body weight per day.⁴⁾Athletes are recommended to consume 1.3 to 1.9 times as much protein as the general public.

In other words, it is very important for athletes to consume plenty of protein in their daily diet in order to maintain sufficient muscle mass.

1) Arata Terada, Sports Nutrition. University of Tokyo Press, pp120-121,2017, XNUMX
2) Thomas DT, Med Sci Sports Exerc 2016;48(3):543-68.
3) International Olympic Committee. Nutrition for Athletes.2012.
4) Dietary Reference Intakes for Japanese (2015 edition)

Muscle breakdown during exercise – amino acids are used for energy

Use of amino acids as energy – Increased consumption due to reduced carbohydrates

In order to exercise, the muscles need to use energy. This energy is produced primarily from carbohydrates and lipids, but amino acids (proteins) are also used in the same way.

Although it varies depending on the person exercising, it is said that 4 to 10% of the total energy used by the body is produced from amino acids.⁵⁾However, if you continue exercising when there is little carbohydrate (glycogen) stored in your muscles, more protein and amino acids will be used to create energy (Figure 3). As a result, you will notice that the amount of burnt remains (called urea nitrogen) that are produced after use is increasing. In other words, the protein in your body that you want to maintain is being broken down and used as an energy source, so you need to be careful.

Decrease in amino acids due to exercise intensity and duration – Decrease in BCAA

Data shows that the more intense or longer you exercise, the more amino acids your body uses up.⁶⁾⁷⁾(Figure 4) We can see that the more intense the exercise and the longer the duration, the more amino acids are used.

Figure 3

Figure 4

In addition, exercise can reduce the amount of certain types of amino acids in the muscles. One of these is BCAA, which is well known among athletes.^8)9)10)11)During exercise, amino acids, especially BCAAs, are used as an energy source and are lost (Figure 5).

Figure 5

As we have explained so far, in muscles, new proteins are constantly being produced and old ones are being broken down at the same time. However, during exercise, new proteins are produced less frequently, while the amount broken down increases.¹²⁾Therefore, when you exercise, the amount of muscle protein that is broken down is greater than the amount of protein that is stored in the muscles. In other words, when you exercise, your muscles gradually decrease, and your condition declines.

5) Lemon PW, J Appl Physiol Respir Environ Exerc Physiol 1980;48(4):624-9.
6) Haralambie G, Berg A, Eur J Appl Physiol Occup Physiol 1976; 36: 39-48
7) DJ Millward, Proc Nutr Soc.1994;53(1):223-40
8) Gibala MJ, Sports Med 2007; 37: 337-340
9) Van Hall G, The Journal of Physiology 1996;494 (Pt 3):899-905.
10) Rush JW, J Appl Physiol 1995;78(6):2193-200.
11) Shimomura Y, J Nutr 2006;136(1 Suppl):250S-3S.
12) AJ Rose, J Appl Physiol 2009

Points about muscles and amino acids

To summarize the above, (Figure 6)

・Muscles are made of amino acids (=proteins).
-Muscle proteins are constantly being replaced!
-That's why it's very important to take in protein (amino acids) every day.
-When you exercise harder and longer, the amino acids in your muscles are also used as an energy source.
When you exercise, less new muscle protein is produced and more is broken down.
As a result, muscle mass is gradually lost during exercise, causing the muscle to lose its condition.

Figure 6

Do you know what happens to your muscles when you exercise?
In order to deliver a performance that you can be satisfied with, try to focus on improving the condition of your muscles.

▼Click here for amino acids that solve this problem
"Essential amino acid mix with high leucine content" maintains muscle condition during exercise and also supports recovery from fatigue after exercise!

<Supervisor>Masaaki Sugita

Current position: Professor, Faculty of Physical Education, Nippon Sport Science University. PhD (Academic)
As a member of the scientific staff of the Japanese Olympic Committee and the Japan Association of Athletics Federations, he has provided medical and scientific support for 30 years, contributing to improving Japan's international competitiveness. He provided scientific support to many athletes, including race walkers and marathon representatives, at the 2010 FIFA World Cup and the London and Rio de Janeiro Olympics. He is currently working energetically on initiatives leading up to Tokyo 2020.