The human body has two main energy systems it gets its power from; the aerobic and the anaerobic system. Most of us have heard these terms, but how many of us really understand how they work?
All human cells use ATP to generate power. Adenosine triphosphate (ATP), is an energy-carrying molecule found in the cells of all living things. ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.
Phosphate, carbohydrate and fat are transformed into ATP which happens at different speeds.
The anaerobic alactic system
No oxygen and no lactate. Sounds like this energy source is not very sustainable? Correct! The body has ATP reserves for about 7 seconds. During that short time it is possible to perform at your max power. Your body does not need to transform carbs or fats into ATP which takes time, but can directly access your ATP and phosphate storage. Afterwards the power output drops significantly. Purposed for fast and powerful movements, the anaerobic alactic energy system is the essential power source for sprinters and weightlifters.
The anaerobic lactic system
Above lactate threshold
No oxygen, but lactate instead. During the final dash when you are out of breath, your legs burn, and you need to give all you got, your body is operating above lactate threshold. Purposed for intense activity, the energy source of this system – also called the anaerobic glycolytic system – is glycogen and lactate.
Because of the lack of oxygen, metabolising fat isn’t really possible. But the body burns carbohydrates even without oxygen. This creates large quantities of lactate which make it impossible to perform for more than one to two minutes at this level. Lactate threshold means reaching the level of intensity where the body starts to create more lactate than it is able to metabolize.
Below lactate threshold
In this case, there is some oxygen in the body and the lactate can be broken down faster than it is created. A typical example of this might be a 10 km run. During those 30 to 60 minutes carbohydrate is the main energy source. The way ATP is created is the same as above lactate threshold. The difference is the lactate is being produced at a rate where it can still be broken down.
The aerobic energy system
This is the main power source for endurance athletes. Why? The aerobic system utilizes carbohydrates, fats and sometimes proteins to generate energy. Aerobic exercise can be sustained for longer periods of time.
At this level, our carbohydrate store lasts for about 90 minutes. After that point the only energy source is fat. Even the leanest athlete has almost unlimited fat resources, but transforming fat into ATP is relatively slow. For endurance athletes it is very important to improve performance in the aerobic zone.
While we can conceptually separate the three systems, it’s important to understand that our body’s cells use all energy sources at all times. What changes is the share each fuel source has on the total energy production. Even at rest the anaerobic lactic system, for example, is working at a low level.
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