Muscle are a band or bundle of fibrous tissue in a human or animal body that has the ability to contract, producing movement in or maintaining the position of parts of the body.

There are three types of muscle tissue: Visceral, cardiac, and skeletal.

But here we will be talking only about the skeletal muscle that is the only voluntary muscle tissue in the human body—it is controlled consciously. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other. These muscles are formed when many smaller progenitor cells also known as muscle fibers lump themselves together to form long, straight, multinucleated fibers.

These muscle fibers can be functionally divided into the following types:-
  • Slow twitch fibers / type- I fibers
  • Fast twitch fibers / type- II fibers
  • Type II a
  • Type II x
  • Type II b

Muscle fiber type is thought to influence the strength-to-size ratio of individual muscles (also called specific tension). Type II muscle fibers are generally believed to display a higher force than type I muscle fibers.

Secondly, muscle fiber type is thought to affect muscle contraction velocity. It has consistently been found by many investigators that type II muscle fibers display a markedly faster muscle contraction velocity than type I muscle fibers.

Thirdly, muscle fiber type is thought to be important for hypertrophy programming. It has traditionally been accepted that type II muscle fibers tend to increase to a greater extent in cross-sectional area than type I muscle fibers following a program of resistance training. However, it has been suggested that observations of greater hypertrophy in type II muscle fibers could potentially be more a function of the type of resistance training programs that are conventionally used to study increases in muscle cross-sectional area than of the responsiveness of this particular muscle fiber type.

These facts play a very important role in selection of the type of game we are going to indulge in. Our muscle fiber type influence what sports we are naturally good at or whether we are fast or strong. Olympic athletes tend to fall into sports that match their genetic makeup. Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who excel in marathons tend to have 80 percent slow twitch fibers. A person with high amount of fast twitch fibers than the slow twitch are expected to be involved in fast and high intensity games and sports and the vice versa is applicable for the other type. But these facts are being ignored in our country and we select our games and sports only on the basis of our interest and not as per our capability. To some extent we can blame our countries financial condition but again we cannot just ignore the lack of knowledge we have regarding this subject matter.

Moving ahead let me introduce you to the basics of the types of muscle fibers :-
  • Slow twitch fibers / type- I fibers – Type I muscle fiber is also known as “slow twitch oxidative” fibers. They are used in lower-intensity exercises such as very light resistance work aimed at muscular endurance and long-duration aerobic activities such as 5K and 10K runs. Type I fibers are identified by slow contraction times and a high resistance to fatigue. Structurally, they have a small motor neuron and fiber diameter, a high mitochondrial and capillary density, and a high myoglobin content. Slow twitch fibers also have a low supply of creatine phosphate, low glycogen content, and a high store of triglycerides (the stored form of fat). Slow twitch fibers contain few of the enzymes involved in glycolysis, but contain many of the enzymes involved in the oxidative pathways (Krebs cycle, electron transport chain). Slow twitch fibers are predominantly used for aerobic activities requiring low-level force production, such as walking and maintaining posture, but are also the primary fiber type found in endurance athletes. Most activities of daily living use slow twitch fibers.
  • Fast twitch fibers / type- II fibers – Type II muscle fiber is also known as fast twitch muscle fiber. These fast twitch fibers can be further categorized into Type IIa, Type IIx and Type IIb fibers.
  • Type II a – Type IIa fibers are also sometimes known as fast oxidative fibres and are a hybrid of type I and II fibers. These fibers contain a large number of mitochondria and Myoglobin, hence their red color. They manufacture and split ATP at a fast rate by utilizing both aerobic and anaerobic metabolism and so produce fast, strong muscle contractions, although they are more prone to fatigue than type I fibers. Resistance training can turn type IIb fibers into type IIa due to an increase in the ability to utilize the oxidative cycle.
  • Type II x – Basically this is a group for a small number of fibers that didn’t clearly belong to the other fast groups. These fibers have fast contraction times and maintain some, though not a great amount of their force production with repeated activity.
  • Type II b – Often known as fast glycolytic fibers they are white in color due to a low level of myoglobin and also contain few mitochondria. They produce ATP at a slow rate by anaerobic metabolism and break it down very quickly. These results in short, fast bursts of power and rapid fatigue. As mentioned above, this type of fiber can be turned into type IIa fibers by resistance training. This is a positive change due to the increased fatigue resistance of type IIa fibers. These fibers are found in large quantities in the muscles of the arms.

From the above discussion we can conclude that Athletic skill comes from a combination of genetics and training, but muscle fiber types play a major role too. Not everyone has an equal distribution of fast-twitch and slow-twitch muscle fibers. Athletes that excel in particular sports frequently have a higher ratio of one or the other and hence we need to excel in the science of myology in order to excel in the field of sports and games.