Bioenergetics
Energy is the ability to do work, and this includes all human movement and activity.
The human body uses energy from food to fuel movement and essential body functions, but the body cells don't get energy directly from food.
After food is digested, the carbohydrates, protein and fat break down into simple compounds -- glucose, amino acids and fatty acids -- which are absorbed into the blood and transported to various cells throughout the body.
Within these cells, and from these energy sources, adenosine triphosphate (ATP) is formed to provide fuel.
The body uses 3 different systems to supply cells with the necessary ATP to fuel energy needs.
Most of the body's activities use a continuum of all three energy systems, working together to ensure a constant supply of energy.
THREE ENERGY SYSTEMS
ATP-PC or Alactic Anerobic or The Phosphagen System (ANAEROBIC)
The phosphagen system kicks into high gear when you FIRST start exercising by metabolizing a molecule called phosphocreatine to produce ATP.
The phosphagen system doesn't require oxygen (making it an "anaerobic system") and works fast, but because your cells don't store a lot of phosphocreatine, its ATP-producing capacity is limited.
TIME LIMIT: Maxes out after only about 10 seconds of exertion
Value of supplementing with creatine- the idea is to keep this system cranking for longer. The body converts creatine to phosphocreatine, and loading up on it through supplementation will help you bang out a couple more high-quality reps.
BUT- even if you keep your cellular stores topped off, you're going to push the limits of the phosphagen system in about the time it takes you to sing the alphabet.
The Lactic Acid or Glycolysis or Glycolytic System (ANAEROBIC)
After about 10 seconds of exertion, your body transitions to the glycolytic system, which is the dominant means of energy production for the next two minutes of exercise. If you're running intervals or doing HIIT, this is your go-to metabolic pathway.
The glycolytic system uses carbs (in the form of blood glucose and stored glycogen) to produce ATP. Like the phosphagen system, it starts out producing energy anaerobically, but as you approach the two-minute mark, oxygen becomes an increasingly important part of the process. After about two minutes, it becomes an absolute necessity.
LACTATE IS NOT LACTIC ACID
MUST WATCH VIDEO!
Excellent Explanation
The Aerobic Glycolysis or Oxidative System (AEROBIC)
That's the point when the oxidative system takes over. Due to the importance of oxygen for energy production in this pathway, it's sometimes called the "aerobic system". The oxidative system uses both carbs and fat in addition to oxygen to produce ATP. While it doesn't produce ATP very quickly, it can produce a lot of it, making this system the preferred one for long-duration, relatively low intensity "cardio" activities such as steady-state runs and bike rides.
To be clear, none of these systems ever "shut off." They're all running all of the time, but the one that's emphasized changes based on your energy needs, which are determined by the intensity and duration of your training. And arming yourself with this knowledge will allow you to optimize your workout performance and results.
ENERGY SYSTEMS SUMMARY CHART BELOW
