Muscle fiber types explained.

      It dawned on me that you cannot have a series about resistance training adaptations without first explaining what muscle fibers are. 

    Generally speaking, muscle fibers fall into two categories: Type 1 and type 2. Type 1 or slow twitch muscle fibers are smaller, have low force production capabilities and contract slowly. These fibers are fatigue resistance and highly oxidative meaning they are slow to fatigue and use oxygen as a fuel source. Due to the use of oxygen, the mitochondria are larger to fulfil the oxygen demands with the Krebs cycle. Since oxygen is used transporting that oxygen needs to be efficient; type 1's have a higher capillary density in order to transport blood more efficiently (along with hemoglobin that transports oxygen). Consider Amazon delivery process; in order for the packages to be delivered in a timely manner drivers need to be hired to drive the product to the location. Similar process for type 1 muscle fibers. We need oxygen to run! I got you fam..... here are some mitochondria to help you produce oxygen and some capillaries to transport that oxygen. Due to the increased oxygen type 1 muscle fibers are often depicted as red. Type 1's are predominantly used in endurance type events such as walking, running long distance, cycling long distance, etc.

     Type 2 muscle fibers on the other hand can be broken down into several different types. I mentioned all of them in a previous article about resistance training adaptations to muscle fibers. For this article I'll mention the more prevalent ones. Type 2a present a mix of oxidative/glycolytic properties that are used more for moderation. They possess properties of type 2 muscle fibers coupled with type 1 properties. They are larger motor units then type 1 and have high nerve conduction. Think about how the mind-muscle connection works in this scenario. When I jump the cerebral cortex sends that signal to the leg muscle to jump it is a fast, powerful response. Since these muscle fibers do not require oxygen, they have low myoglobin levels. These are used in repeated jumps, lifting heavy weights and sprints.

    Another category of type 2 muscle fibers is your Type 2x which are your largest muscle fibers that are extremely low fatigue resistant meaning they tire out quickly. Since the force is so high is has the highest recruitment rate amongst the muscle fibers. More rest is required to restore the muscle to full capacity as well. They are also white in color because they do not use oxygen in order to contract. Type 2x have the lowest capillary density and the lowest mitochondria. These are your weight jumps, resistance training in repetitions of two to three and your short distance sprints like hill sprints.   

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