L4_Where does your energy come from?

-----Discovering the human body’s three main energy supply systems

In this chapter, we will discuss an important and interesting topic: Where does the energy that supports your exercises and daily life come from? If there are multiple energy supply systems, how do they work in different roles?

First, lets list the main energy supply systems: The human has three main energy supply systems, there are:

The ATP-CP(also known as non-lactic acid) system;

The glycolysis(Also known as lactic acid) system;

Aerobic oxidation system

The three main systems work simultaneously, but the proportion of energy they provide within a certain period of time is determined by the intensity of the exercise being performed, and we will explain them one by one in the following text.

Main Energy Substances of the human body

Before that, let's first understand the main energy substances of the human body that will be mentioned in the following text:

1. ATP: ATP (adenosine triphosphate) is the most fundamental energy molecule in the human body. It consists of one adenine base (adenine), one ribose molecule, and three phosphate groups. ATP stores and transmits energy within cells, serving as the foundation of all biological activities and the most direct energy source.
   

2. CP: CP (creatine phosphate) is a molecule that stores high-energy phosphate compounds. It is mainly stored in muscle cells and reacts with ADP (adenosine diphosphate) to form ATP through phosphate transfer, thereby providing energy. CP can quickly decompose and convert into ATP, providing energy for high-intensity, short-term exercise.
   

3. Glycogen: Glycogen is a polysaccharide body primarily stored in the liver and muscles. It is composed of multiple glucose molecules connected and can be broken down into glucose when energy is needed, producing ATP through glycolysis and aerobic oxidation. Glycogen is one of the main energy sources for anaerobic glycolysis and aerobic oxidation systems, providing the energy needed for moderate intensity, medium to long duration exercise.
   

4. Fat: Fat is the most abundant form of energy storage in the human body. Fat is stored in adipocytes in the form of triglycerides. In aerobic oxidation systems, fats are broken down into fatty acids and glycerol, which are further oxidized to produce ATP. Fat is one of the main energy sources in the aerobic oxidation system, providing the energy needed for long-term, low-intensity exercise.

Energy supply systems

 1. ATP-CP (non lactic acid energy) system

Features: No need for oxygen (can also be done under aerobic conditions); High output power and short maintenance time (6-8 seconds); Recovery time 3-8mins

This system mainly provides a large amount of energy to the human body in a short period of time through ATP. The ATP-CP system is the fastest energy supply system in the human body, and this process does not require oxygen to participate, hence it is called anaerobic energy supply.

The time for ATP to release energy for muscle contraction is only 1-3 seconds. And CP decomposition can provide energy, help ATP synthesis quickly, maintain ATP content at a relatively constant level in the first few seconds, and continue to maintain muscle activity.

Unfortunately, the content of CP in muscles can only sustain 6-8 seconds of muscle contraction after the synthesis of new ATP. As the CP content decreases continuously for ATP synthesis, both ATP and CP content significantly decrease during exhaustion, insufficient to continue providing energy to maintain muscle contraction and relaxation.

Therefore, short-term, high-intensity activities (such as weightlifting, sprinting, etc.) mainly rely on the ATP-CP system to supply energy for muscle contraction.

2. Glycolysis (lactic acid energy) system

Features: No need for oxygen; The output power is moderate and the sustain time is moderate (1-3 minutes); Recovery time: 30-180s

The anaerobic glycolysis system refers to the production of energy through sugar decomposition in the absence of oxygen. When muscles require energy, glycogen (a stored form within the muscle) is broken down into glucose and ATP is produced through glycolysis.

ATP releases energy for muscle contraction. This metabolic process can provide about 1-3 minutes of muscle contraction time.

This process is relatively slow compared to ATP-CP systems, but can provide energy for a longer period of time. The anaerobic glycolysis system is mainly used for moderate intensity, medium to long duration sports such as basketball, soccer, etc.

3. Aerobic oxidation system

Features: Requires a large amount of oxygen consumption; Low output power, long maintenance time

The aerobic oxidation system is the most persistent energy supply system, which generates energy through metabolic processes involving oxygen. In this system, nutrients such as glucose, fat, and protein are broken down by oxygen to produce ATP. The speed of aerobic oxidation system is slow, but it can provide sustained energy for a long time. This system is mainly used for low-intensity, long-term sports such as long-distance running, swimming, etc.

Below is the relationship between exercise time and output power of the energy supply systems:

It can be seen that in short-term high-intensity sports such as sprinting and weightlifting, the energy provided by the ATP-CP system is the most important. This is because ATP-CP systems can quickly generate energy, but have limited storage capacity.

As exercise time prolongs, the energy reserve of the ATP-CP system gradually depletes, and the anaerobic glycolysis system begins to take effect. When the exercise time is further extended, the aerobic oxidation system becomes the main energy supply system.

The following is the relationship between exercise time and the proportion of energy provided by the energy system:

It can be seen that in short-term high-intensity exercise, the ATP-CP system has the highest proportion of work. With the extension of exercise time, the proportion of anaerobic glycolysis system gradually increases, while the proportion of ATP-CP system gradually decreases. Finally, during prolonged exercise, the aerobic oxidation system becomes the main energy supply system, with the highest proportion of its work.

And below is the main energy supply systems for each time period of exercising.

Maintained Time	Exercise intensity	Main Energy Supply System	Examples
0-6s	Extremely high	ATP-CP system	100m run
6-30s	Very high	ATP-CP system and glycolysis system
30s-2min	high	Glycolysis system	800m run
2-3min	average	Glycolysis system and oxidation system
>3min	low	Oxidation system	10000m run
---	none	Oxidation system(Mainly fat oxidation)	Doing no exercise

These relationships are based on common theories and research results in exercise physiology, but the specific values and curves may vary due to individual differences, exercise types, and intensities. If you want to obtain more accurate and specific information, it is recommended to refer to relevant authoritative research papers or consult professional exercise physiologists or exercise scientists.

In short, the significance of understanding the three major energy supply systems in the human body is to help you understand what elements you are consuming in your body under different exercise modes. By further expanding your knowledge, you will be able to independently design your diet, training, and even life plan; Or have a more three-dimensional understanding of exercise intensity. Exercise is a matter of living within one's means. It is important to have a comprehensive understanding of one's body and consciously prevent risks. Taking good health precautions is of utmost importance.

Next, we will have more articles that explain different common knowledge and common misconceptions about sports in a simple and easy to understand way:

Sources and references cited:

Jason Karp, PhD. “The Three Metabolic Energy Systems.” IDEA Health & Fitness Association, 5 May 2021, www.ideafit.com/personal-training/the-three-metabolic-energy-systems/.

Author    Christopher Gagliardi    Contributor                  Chris Gagliardi is an ACE Certified Personal Trainer. “The Three Primary Energy Pathways Explained.” Energy Pathways | 3 Primary Energy Pathways in the Body | ACE Blog, www.acefitness.org/fitness-certifications/ace-answers/exam-preparation-blog/3256/the-three-primary-energy-pathways-explained/. Accessed 6 Aug. 2024.