Anyone wanting to optimise fitness, sports and even life performance and quality shall understand where we get the energy from and how our body deals with it.
Ultimately, the energy that keeps us moving comes from the food we eat. However, we cannot use energy directly from food.
It must first be converted into adenosine triphosphate, or ATP, the immediate useable form of chemical energy utilized for all cellular function. The body does store a minimal amount of ATP within the muscles, but the majority is synthesized from the foods we eat.
Food is made up of carbohydrates, fats and proteins, and these nutrients are broken down into their simplest forms (glucose, fatty acids and amino acids) during digestion. Once these nutrients are broken down, they are transported through the blood to either be used in a metabolic pathway or stored for later use.
Because we do not store a significant amount of ATP and need a continuous supply, it must be constantly resynthesized. This occurs in several ways using one of three energy systems:
ATP-PC System or Alactic System
Anaerobic (somewhat slow, uses carbohydrates)
Aerobic (slow, uses either carbohydrate or fat)
Overview of the 3 Energy Systems
Adenosine tri-phosphate (ATP) is the only energy source for all bodily functions and activities (movements)
When ATP is used for energy production it must be replenished
The body can replenish (recreate) ATP aerobically or anaerobically
There is one Aerobic Energy System which requires oxygen to replenish ATP and two Anaerobic Energy Systems that can recreate ATP to produce energy (without the need of oxygen)
These are the 3 Energy Systems
ATP-PC System or Alactic System – ATP and creatine phosphate (CP) are present in very small amounts in the muscle cells. The system can supply energy very quickly because oxygen is not needed for the process. No lactic acid is produced in the process (Alactic)
Anaerobic Glycolysis or Lactic Acid System uses carbohydrates (glucose) stored in the muscles as Glycogen. Because no oxygen is required to re-synthesise ATP, energy is produced quickly. Also because no oxygen is used in the process lactic acid is produced as an end product.
Aerobic System – This system uses carbohydrates (glucose/glycogen) and fats to replenish ATP. Because oxygen is required for the process, energy production takes a little longer but can continue for a much longer duration. Because of the presence of oxygen, no lactic acid is produced.
Intensity, duration and fitness levels
The 3 energy systems are all working at the same time to keep replenishing ATP (At no point only one energy system will be used).
Yet, there is most commonly a predominant system.
The predominant energy system used during exercise will depend on the intensity and duration of the activity and the individual’s levels of fitness:
Intensity of exercise. (How hard you are working). The more intense the exercise the greater amount of (Anaerobic Energy) – Creatine phosphate and muscle glycogen will be used. Low to medium intensity exercise will use predominantly the aerobic system
Duration of exercise. (How long you are exercising). E.G. If the exercise is high intensity and lasts over 2 minutes then both CP and Muscle Glycogen will become depleted and need repaying. Intensity of exercise will drop as the aerobic system becomes more dominant.
Fitness level of the performer. Individual levels of both aerobic and anaerobic fitness will impact on the predominant energy system being used. A higher level of aerobic fitness will mean it will take a performer longer to reach the Anaerobic Threshold (The point at which the performer gets more energy from the anaerobic systems rather than aerobic). This is beneficial because when a performer begins to work anaerobically there is only a limited supply of energy available (PC and muscle glycogen - up to 2 minutes max). If the exercise continues to increase then the performer will run out of anaerobic energy and return to using aerobic whereby performance will then drop. This can be seen at the last few stages of the multi stage fitness test where the performer struggles to stay in time with the ‘beeps’ and eventually has to stop. The greater the anaerobic fitness the longer the performer can work in the anaerobic zone. In reality most people have anaerobic stores that last just over a minute. A trained performer can last up to 2 minutes, and also be able to ‘tolerate’ greater amounts of lactic acid in their muscles.
Sport specific simple examples and practical application
ATP-PC system is predominantly used during maximum intensity activities lasting no longer than 10 seconds such as weight lifting and power lifting, 100m (or less) sprint, etc.
Anaerobic Glycolysis system is predominantly used for high intensity activities lasting approximately 1 minute such as surfing, 400m sprint, most gymnastics types, diving, etc
Aerobic system is predominantly used during medium to low intensity activity such as marathons, over 1km run, skating, cross-country skiing, etc
The predominant energy system being used at rest is the aerobic system.
The energy continuum below illustrate well the percentage of the energy systems use during some sport. However, remember that the energy systems are all working at the same time to keep replenishing ATP (At no point only one energy system will be used). Hence, the bellow chard is solely use as general guide.
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The above are general guileless which surely will help you to choose the correct training programs and platforms for your sport specific requirements. Nonetheless, if you are serious at becoming a better athlete, I strongly recommend to seek a professional sport specific fitness coach. We certainly, CAN help:
Tomás Agustin Würst, Fitness Trainer, Yoga Teacher and Manager Director at Workout Australia.
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