The Lactic Acid System, also known as the anaerobic lactic system, is the subject of this article. As described in the first part of the body’s energy systems, we need a constant supply of energy to function properly and to stay healthy. The body receives energy from what we eat in the form of carbohydrates, proteins, and fats.
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We mainly use carbohydrates and fats as energy sources in the body. The energy contained in these substrates is chemically released in the cells and stored in a high-energy compound called adenosine triphosphate (ATP). Basically, we need ATP to realize muscle contractions (both muscle contraction and relaxation). Therefore, the body has different ways to generate ATP.
The Phosphate System
The first energy system described is the ATP-CP system, also called the phosphate system. This is the easiest and fastest way for the body to generate ATP, and it happens without the presence of oxygen (anaerobic). In this process, carbohydrates and fats (also no proteins) are not used. This way of generating ATP mainly occurs during very intensive forms of training. Think, for example, of short sprint activities (100m), powerlifting, but also high and long jumps. This method can only provide energy to all muscles for 10 to 15 seconds, after which exhaustion occurs. It is also not possible to store large amounts of ATP in the muscles, only a small amount for a few seconds of intensive activity.
Here is a brief overview of the three different energy systems:
1. ATP-CP system / phosphate system
2. The Anaerobic system / lactic acid system
3. The Aerobic system
Anaerobic Lactic System, or “Lactic Acid System” (Glycolysis)
The second energy system is the anaerobic lactic system, also known as the lactic acid system. In this way, ATP is produced by breaking down glucose (which is made from ingested carbohydrates). Before glucose or glycogen (stored form of glucose in muscle and liver cells) can provide energy, they must first be broken down into glucose-6 phosphate. The conversion of glucose to glucose-6 phosphate requires an ATP molecule. This is not the case with glycogen. So, each unit of glucose yields 2 ATP and each unit of glycogen yields 3 ATP. The product of this reaction is lactic acid, which is converted back into glucose via the liver.
This system is able to provide energy for a longer period than the phosphate system (ATP-CP system). Due to the accumulation of lactic acid, this is also limited to only 30-50 seconds of energy. When more lactic acid is produced than converted into glucose, it accumulates in the muscles. This is the familiar feeling of “acidification”. You then need to rest until more lactic acid is converted into glucose. The point at which as much lactic acid is broken down as is produced is called “the tipping point” or “the anaerobic threshold”.
This system is particularly active when, for example, you try to do as many push-ups as possible in a row. Or, for example, during a 400-meter sprint. You will notice that after a while, it just starts to hurt. This feeling known as acidification is not caused by lactic acid itself, but by the hydrogen ions that are split off as a result. These hydrogen ions accumulate and lower the pH of the muscles, preventing them from contracting. You will then notice that you have to take it easy. The body only needs a short time to remove these waste products, after which you can continue with your training.
Also read the article: the functioning of muscles
Training and the Anaerobic Lactic System
The more you train on the energy supply of this system, the better your body is able to buffer these hydrogen ions. In addition, training with moderate to high intensity ensures that your body recovers faster. During strength training in the gym, you make much use of the Anaerobic lactic system. The typical 8-12 repetitions that many people choose during strength training mainly use this energy system because of the high intensity and duration of the exercise.
Improving the anaerobic lactic system mainly happens by increasing the anaerobic threshold. Especially runners do this by calculating this tipping point based on their heart rate during endurance runs. By training around this tipping point, the body becomes faster at converting lactic acid into glucose, allowing for longer performance before experiencing acidification.
Two of the three energy systems are now described. It is important to understand that all these systems are always active together. The duration and intensity only determine which system is most active. For efforts with a moderate to high intensity and a duration of up to 30-50 seconds, most of the energy comes from the Anaerobic lactic system, with energy being supplied from the ATP-CP system for the first 10-15 seconds.
Summary
The body has various ways of supplying energy. The phosphate system or ATP-CP system, the anaerobic lactic system or lactic acid system, and the aerobic system. The extent to which these different energy systems are used depends on the duration and intensity of activities. For activities lasting up to 30-50 seconds with a fairly high intensity, mainly the anaerobic lactic system is used. This system can provide energy less quickly than the phosphate system but can provide energy for a longer duration. Training focused on this system primarily improves performance at a moderately high intensity with a duration of up to 50 seconds. However, this energy system cannot supply nearly as much energy as the Aerobic system. The next part will delve deeper into this last energy system.
References
NASM Essentials of Personal Fitness Training
The Three Metabolic Energy Systems by Jason Karp PhD
All About your Metabolic Energy Systems by Andrew Heffernan
