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Energy System Development: Part Three

Jan 21, 2014

Energy System Development: Part Three

Thus far in our discussion of energy system development we have covered the three energy systems, how to train them and which ones are primarily utilized with variations in the time and intensity of the exercise being performed. Now it’s time apply that knowledge to specific modes of physical activity, in particular various sports. But first, we need to cover muscle fiber types and their role in energy utilization.

Along with the three energy systems there are three different muscle fiber types; type I (slow twitch), type IIa (fast twitch) and type llx (fast twitch), each having distinct performance characteristics. Type I muscle fibers are fatigue resistant, efficient and rely heavily upon the oxidative energy system and have little reliance on the phosphocreatine energy system. Therefore individuals who have predominantly type I muscle fibers tend to have better endurance yet are not very explosive, although training can help change this. Both type II muscle fiber types rely more heavily on the phosphocreatine energy system and are much quicker to fatigue and less efficient than type I muscle fibers. Type II fibers are much more explosive and have higher anaerobic capacity than type I. Between type IIa and IIx, type IIa have a greater resistance to fatigue. Therefore individuals who are type II dominant will tend to be more explosive but fatigue much quicker then individuals who are type I dominant. All humans have all the fiber types, for example postural stabilizing muscles are vastly composed of type I fibers while larger muscles such as the quadriceps are composed of a larger mixture of the two to allow for greater variations in levels of power output, i.e. walking and sprinting. With that being said, some people tend to be more type I dominant and others may be more type II dominant.

Although individuals are genetically predisposed to be more type I, IIa or IIx dominant, with training, they can alter their fiber types to a certain extent. Type IIa fibers are the fibers that can change to become either more aerobic like type I or more anaerobic like Type IIx. Therefore the amount of type IIa fibers an individual has will determine how much of a change they can make via training. Individuals training for a specific goal or event i.e. to be fast or to run a marathon should have vastly different training programs in order to elicit the necessary physiological changes. But before one begins building their training program they must first layout their goals and the physiological demands their body will face.

Below is a preview of next month’s blog where we begin to cover various sports and their specific energy system demands.

Almost all sports will rely heavily on the phosphocreatine system aside from ultra-endurance events that lack explosive movements, such as; long distance running i.e. marathons, long distance swimming and cross-country skiing. Those sports lacking explosive movements will rely heavily upon the oxidative energy system with a low to moderate reliance on the glycolytic energy system depending on the intensity and duration of the activity.


Baechle, T. R., & Earle, R. W. (2008). Essentials of strength training and conditioning . (3rd ed.). Campaign, IL: Human Kinetics.


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