Aerobic vs. Anaerobic vs. ATP-PC
Any quality of movement an athlete makes (explosive, sustained high-intensity, or endurance) uses one of three types of energy systems. They are aerobic, anaerobic, and ATP-PC, and what distinguishes them is the required quality of movement to do such exercise.
Aerobic system is the body's most sustainable use of energy (used for endurance). As a result the exercise being a sustainable pace, it uses oxygen to break down carbohydrates and fat for an extended time. In simple terms the exercise is long enough and sustainable enough that you have time to take in oxygen, and your body has enough time you convert it to energy. This process produces no fatiguing byproducts, such as lactic acid, meaning that this sustained effort can be maintained for a long time. If an individual has a well conditioned aerobic system, their ability to recover between high-intensity efforts increases, meaning the athlete will be able to train harder for longer. An example of a sport that is heavily reliant on aerobic fitness is long distance running, swimming, and cycling. Often called zone 2 training, or steady state.
Anaerobic system produces energy quickly without oxygen by breaking down glycogen, as a result of this, the byproduct produces lactate acid. This process causes the literal burning sensation during anaerobic exercise. This is the dominant system for efforts lasting between 10 seconds to two minutes. What makes this system what it is, is that the effort is too hard for the aerobic system to keep up but too long for ATP-PC stores to cover. In simple terms, this is the system that is responsible for sustained power. An example of a sports that is heavily reliant on the anaerobic system is 400m running, wrestling, 2km rowing.
ATP-PC (adenosine triphosphate-phosphocreatine) system is the fastest and most explosive of the three. To make it easier to understand, ATP (adenosine triphosphate) is the molecule that directly powers muscle contraction. It is important to know that they body does not have a lot of ATP at any given time, which is why this system is built for short, explosive movements. Once ATP begins to run low, PC (phosphocreatine) breaks apart into creatine and a phosphate molecule releasing a phosphate molecule which later creates more ATP for the body to use. This sounds more complicated than it is, but it means the the body does not have a lot of explosive energy (ATP) and that's why it is used very quickly. PC creates a new ATP fairly quickly, so it only takes 3-5 minutes to fully recover. Another side note, is that athletes with a higher aerobic fitness fully recover quicker than those who are not as aerobically fit. This system also produces no waste product, meaning no lactic acid is produced. An example of a sports that is heavily reliant on the ATP-PC system would be olympic weightlifting, powerlifting, and 100m sprint.
Bigger Picture
Understanding the bigger picture is as important as knowing each system on its own, because in practice, none of them work in isolation.
It is not physically possible to 'turn off' a system whilst doing exercise. At every moment, your body in drawing energy from all three systems, what changes is how much each one contributes based on the intensity and duration of the effort.
Yet understanding when each system is most prevalent, allows athletes to optimise training adaptations, and better understand the physiological factors that influence performance.
