Tuesday, 5 August 2008

What Are We Made For?

By: Mujuthaba


One of the major indicators of what a training outcome is the type of skeletal muscles a body is made of. The skeletal muscles of the human body are made of two types of muscle fibers. They are categorically known as Type-I and Type-II fibers or slow twitch and fast twitch fiber respectively.


The Type-II fibers have two subtypes; Type-IIx and Type-IIa. Earlier Type-IIx was referred to Type-IIb. This specific type contains the fastest twitch characteristic of any muscle fiber and was initially discovered in animals as Type-IIb. This discovery lead to the fastest human skeletal fiber also to be referred as Type-IIb. Although, recent day laboratory studies showed the fastest human skeletal muscle fiber is Type-IIx rather than Type-IIb, which is also similar to rodents.


The distribution of the two types of muscle fibers is congenital. Humans skeletal muscles either have a higher percentage of Type-I or Type-II muscle fibers. An individual built of predominantly Type-I muscle fibers can perform well in low intensity long duration activities, such as long distance running. An individual with more Type-II muscle fibers is suited for high intensity short burst activities. Physiologically, Type-I fibers are much darker (red) in color due to a high capillary density compared to Type-II fibers.


Individuals with predominantly Type-I muscle fibers are usually lean (as in marathon runners). This is due to the small size of the Type-I muscle fibers, and its slow and ineffective adaptation to hypertrophy (increase in muscle size) training.


In contrast, Type-II individuals are quite bulky (as in sprinters). This increased size is due to the larger diameter of Type-II muscle fibers. Hence it will be much easier for individuals containing predominantly Type-II muscle fibers to build muscles and would be assumed to have a promising career as a body builder.


So how do we know what type of muscle fiber dominates our skeletal muscles? If you are a frequent exerciser, you would have an idea of what you are made of. You can either run for a longer duration or either you can do short burst sprints much better than the other. It is impossible for a 100m sprinter to compete with a marathon runner and vice versa. The other easiest way is to test both types of training modes and compare the outcome.


The most accurate way of indicating the composition of skeletal muscle is through muscle biopsies. This is a surgical procedure where a bit of the muscle is torn by a specialized needle inserted into a muscle group. This procedure is done in laboratory settings to conduct studies and on professional athletes, and is not pleasant.


Concluding the types of activity or sport that are best suited for you is not rocket science. The chance is that you already know what your skeletal muscle fibers are composed of, i.e. you know what you are good at. Just follow your instinct and your trainer on it.

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