Energy Systems 101: Get More out of Training.

Energy Systems 101: Get More out of Training.


WARNING: This will be more scientific based, providing the background that some may find helpful. But if you want the simple application Check out Part 2!

For all you scratching your head on what I am referencing when I say "energy systems", think back to your high school days or college days when you heard the terms: 

  • Phosphagen (immediate source)
  • Anaerobic / Glycolytic (somewhat slow, uses carbohydrates)
  • Aerobic (slow, uses either carbohydrate or fat)

3 in total and neither working independently of the other REMEMBER THAT.

Bioenergetics  is the essential terminology that governs energy systems. This fancy term is basically the conversion of chemical energy to mechanical energy. Even simpler, the conversion of carbs, proteins, and fats (chemical energy) into biological energy (mechanical), AKA what gets used during training sessions.

Our lovely bodies are constantly cycling through being anabolic ("building up") and catabolic ("breaking down"). Metabolism is the sum of all the anabolic and catabolic reactions in our body. The energy from catabolic reactions is used to push anabolic reactions, by using ATP (I know you remember that atleast) adenosine triphosphate.  Without ATP, muscle activity and growth cannot occur, plain and simple.

Now, for the sake of this article all that needs to be known about ATP is that: From the foods we eat, potential energy (stored) exists within cells in the chemical bonds such as glucose, glycogen (storage form of glucose) and fatty acids. When these compounds enter energy pathways, some are rearranged with energy released and captured in the formation of ATP (Catabolic). This “new energy” is then used for cell functions such as supplying the energy for muscle contraction (like heavy ass lifting). Since muscle cells can only store ATP in limited amounts, and activity requires a regular supply, energy systems are needed for muscular/bodily function. 

Once again, we are not going to go too in-depth so just remember: 
  • Some metabolic pathways will require oxygen. They are said to be aerobic and will not proceed unless oxygen is present in sufficient concentrations.
  • Other processes don’t require oxygen to proceed to completion and are said to be anaerobic.

This information is worth noting going into our next section. 


PHOSPHAGEN SYSTEM ( 0 -10 Seconds of Effort)

This is the system most related to short-term, high intensity activities, and because a large amount of power is needed to be produced by the muscles there is a high demand for ATP. The phosphagen system is the quickest way to resynthesize ATP and is going to be active at the start of all types of training regardless of  the intensity. Sidenote,The creatine kinase (enzyme) reaction regulates the breakdown in creatine phosphate. (Dont worry if you're a little lost)

Simply, at the start of training, ATP (Energy Currency) is broken down into ADP, and releases energy for muscle contractions. Following the elevation in ADP.. The creatine kinease (enzyme) reaction activates in order to promote the formation of ATP from the breakdown of creatine phosphate. If training continues at high enough intensities, this enzyme reaction (CK) will remain elevated. However, once training is over or subsides to a low enough intensity, glycolysis or the oxidative (mitochondrial respiration) system wil help to supply adequate ATP for muscle energy demand.

Note that ATP and creatine phosphate are stored in the muscle in small quantities, therefore the phosphagen system can’t supply enough energy for continuous, long duration training.


Creatine Phosphate (CP) which is stored in skeletal muscles donates a phosphate to ADP to produce ATP(Adenosine TRIphosphate) . This process does not require oxygen to resynthesize ATP because it is anaerobic or oxygen independent.

This is the primary energy pathway that creatine monohydrate supplementation is based upon. Creatine supplementation is highly effective in the rapid regeneration of ADP to ATP from the creatine kinase reaction during and following intense exercise. Which is why Creatine is touted for its enhancements in exercise capacity and performance. 

GLYCOLYSIS (Begins around 6 & 30 sec for "fast glycolysis", Up to  120 sec if the exercise is low enough in Intensity)

Glycolysis becomes the primary ATP source during high intensity muscular work lasting from thirty seconds to about 2–3 minutes. This system is the second fastest way to resynthesize ATP. Glycolysis, as the name implies functions on breakdown of glucose, and is by far one of the most studied metabolic pathways in the field. 

During glycolysis, carbs in the form of either blood glucose or muscle glycogen (the stored form of glucose) get broken down through a series of reactions to form pyruvate. (glycogen is first broken down into glucose through a process called glycogenolysis blah blah).

Fast forward to the end stage of glycolysis via the breakdown of glucose, you end up with two pyruvate and two ATP. Pyruvate can then go two directions: conversion to lactate (Fast Glycolysis) during higher intensity exercises (anaerobic) or conversion to acetyl coenzyme A (acetyl-CoA), which enters the mitochondria for oxidation and aids in the production of more ATP (Slow Glycolysis). 

This system is also responsible for that "lactic" acid burn you feel after a tough set of lifting weights or an all out 400 m dash. Truth is, it's not "lactic" acid that causes the burn it's the deficiency of oxygen not being fast enough to meet the demands of the effort. This Results in an increase in hydrogen ions, leading muscle pH to decrease (called acidosis) and other metabolites. 


This system is perhaps the most complex, but nevertheless the third and final system that is the primary source of ATP at rest and during low-intensity activities. The usage of mainly carbohydrates and fats are utilized within this system, at rest you are mainly using fats compared to the carbohydrates until the intensity increases. Just like with glycolysis, glucose is transported into the mitochondria where it is taken into the Krebs cycle for ATP. Glucose can also be broken down and cycled into the electron transport chain for ATP production. Note that this system is the slowest for production of ATP, BUT has the greatest capacity for it. You will get more ATP during this system, however it cannot keep up with demands of higher intensity exercise, therefore this system is the source of ATP at activities lasting longer than 3 minutes. 

// Part Two Next.


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