Chapter 2: Energy Systems

Chapter 2: Energy Systems

It is important to understand the role of energy systems in training. While your role as a nutrition coach may never be to prescribe the energy system work to your clients, you must understand the physical demands of their training from an energy system perspective so that you are providing the proper fuel and/or recovery.

The energy that our body produces for exercise and living is a sequence of chemical reactions with the final product being the breakdown of macronutrients (protein, carbs and fats) by which energy to move is produced. There are two main energy pathways Aerobic and Anaerobic. The Aerobic utilizes the transport of oxygen while Anaerobic requires no oxygen and utilizes the creation of ATP or adenosine triphosphate and CP Creatine Phosphate.

The body is not very efficient at trapping energy. The body only traps 20% of its energy as the other 80% is released as heat. Which explains why the human body heats up so quickly when it exercises. When looking at the body’s muscle anatomy it is important to understand the mode of energy storage and energy systems that it uses for a certain type of physical activity.

ATP or adenosine triphosphate is the molecule that stores energy in the form that the body uses for muscle contractions. ATP is the energy source for all human movement. Therefore energy creation centers on rebuilding the ATP molecules after they are broken down during consumption. The body’s muscles stockpile a limited amount of ATP and during exercise our bodies require a constant source of ATP to provide the energy required for muscular contractions. Hence, pathways must exist inside our cells with the ability to create ATP quickly so we can continuously move and our muscle cells can create ATP, thus creating energy by any one of or in combination of the three primary energy systems(ATP-PC Pathway, Glycolytic Pathway and Oxidative Pathway).


During the first few seconds of exercise, regardless of the intensity, the ATP-PC system is called on directly. The energy comes from the breakdown of adenosine triphosphate (ATP) in the muscles.

Unfortunately, the ATP stores last for a mere seconds before needing assistance from the phosphocreatine (PC) or creatine phosphate stores. In combination, this energy system will provide at most 10-15 seconds of work before you shift to your glycolytic system.

Recovery of the ATP-PC system is usually 2-3 minutes in duration. This is why you see a lot of sprint protocols calling for 10-15 seconds of work followed by “maximal recovery” in the 2-3 minute window – as they are following a 1/10-12 work to rest ratio. This allows us to truly train peak power output.

Examples of strength and power movements where the energy produced is coming from immediate ATP stores include: shot put, Olympic weight lifts, high jump, a golf swing, a tennis serve or any activity lasting 0-3 seconds of max out effort.

Examples of sustained power movements where the energy produced is created from immediate ATP and CP stores include sprints, fast breaks in basketball, standard football plays, or any activity lasting about 0 to 10 seconds of max out effort. Although a portion of these movements and exercises also utilize the glycolytic pathway as well.

The Glycolytic Pathway

Once the ATP/CP reserves have been exhausted in the ATP/CP pathway, the body must then move onto breaking down carbohydrates to produce more ATP. It does so by either breaking down muscle glycogen or blood glucose and then converting the ADP (adenosine diphosphate) back into ATP with the unwanted leftover product being lactic acid. That lactic acid by-product ultimately builds up more quickly than it can be cleared out of the muscle to the point that muscles reach what is called the anaerobic threshold or the lactic threshold. At this point, the individual must slow down or stop in order to let the body remove the lactic acid build-up. That removal process is really more of a conversion by which the body converts the lactic acid into lactate of which is used to produce more glucose.

Stored fuel or sugars are usually never completely exhausted in the glycolytic pathway. Nevertheless, the limiting factor is the accrual of the lactic acid. Just like the ATP/CP pathway, the glycolytic pathway is an anaerobic pathway not requiring oxygen to proceed. In most conditions, the glycolytic pathway ends under maximal conditions around 80 seconds before the body transitions into the oxidative pathway and a lower level of exertion proceeds.

Examples of movements where the energy produced utilizing the glycolytic pathway involving the utilization of ATP, CP and lactic acid include: 400-meter dash, 100-yard swim, a 10 rep max lift; or any activity lasting about 1 – 2 minutes.

A few factors that are specific to the individual regarding how your muscles function in the glycolytic pathway are:

  • How does the individual tolerate the pain caused by the lactic acid?
  • How fast the body can buffer out the lactic acid (a measure of how much oxygen you can take in per breath)? (Rich Froning has a V02 of 73)
  • How long one can go before they hit their own lactic threshold?

Again, research shows that training can increase the rate at which lactic acid is cleared from the muscle as well as forcing forward the body’s anaerobic threshold. But then again, a person’s ability to tolerate pain will always be a subjective measure. As experience shows the body’s ability to deal with more pain comes with experience.

Examples of training in the Glycolytic Pathway

A training regimen in this system is again a short one. Like something including quick intervals with a duration of 30 seconds to 2 minutes with a rest period that is twice as long as the interval work period for recovery.

  • 8–10 intervals. Involving a 30 second go with a 1 minute recovery period
  • 4 intervals of work lasting 90 seconds with a 3 minute recovery period

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