Muscle Hypertrophy – The Muscle Fibers Involved

Muscle hypertrophy is the process of enlarging the muscle cells by the initiation of external stimuli that frequently occurs in the body. These stimuli are usually gained from activities such as exercise, workout and bodybuilding. These activities require great demand in the muscle cells. The muscles are forced to meet up these demands however; muscle cells also have their limits. In order to facilitate the achievement of this requirement the muscle cells initiate the mechanism of hypertrophy. Energy is primarily produced inside the cell through an organelle we call as mitochondria. It is known as the powerhouse unit of the cell wherein ATP or Adenosine Triphosphate is produced. It is compound used by the body in order to generate energy. As the body exerts more effort in the activity, these mitochondria produce more ATP in order to provide more energy. If the muscle cells sense the energy being provided by the mitochondria is not yet enough, it induces muscle hypertrophy in response to the said situation. The body increases the size of the muscles in order to provide the additional demand.

The process of muscular hypertrophy depends on the frequency of external stimuli induction, the energy produced and the type of muscular fiber involved. Skeletal muscle fibers are classified into two major types, which are the Type 1 (slow-twitch), and the Type II (fast-twitch fibers). The two fibers differ in terms of metabolism, contractile velocity, neuromuscular differences, glycogen stores, capillary density of the muscle, and the actual response to hypertrophy.

The Type 1 slow twitch muscle fibers have an oxidative property and are mainly responsible for maintenance of body posture and skeletal support. An example of this slow twitch muscle fiber is the soleus, which is a powerful muscle in the back part of the lower leg. An increase in capillary density is connected to Type I fibers because they are more involved in endurance activities. Endurance activities focus more on increased activity time and frequency. These activities are suited for these fibers since they are able to generate tension for longer periods. Type I fibers do not require excessive excitation to cause a contraction. It utilizes fats and carbohydrates more efficiently because of its capacity for oxidative metabolism. Type 1 muscle fibers are developed by the resistance exercise but aerobic exercises also contribute to its increase.

Type II fibers are usually found in muscle sites wherein greater amounts of force production for shorter periods of time are required. Examples of these are the gastrocnemius and vastus lateralis located in the lower extremities. Type II fibers are classified into Type IIa and Type IIb muscle fibers.

Type IIa fibers, also known as FOG or Fast twitch Oxidative Glycolytic fibers, are hybrids or combination between Type I and IIb fibers. They require anaerobic, reactions which produce energy that do not require oxygen instead it uses other resources available and oxidative metabolism in order to support contraction. It involves resistance training and endurance training. On the other hand, Type IIb fibers are also called FG or Fast-twitch Glycolytic fibers. These fibers require mainly anaerobic metabolism for energy for muscular contraction. This is the main reason why they have high amounts of glycolytic enzymes. These fibers generate the greatest amount of force due to an increase in the size of the nerve body, axon and muscle fiber, a higher conduction velocity of alpha motor nerves, and a higher amount of excitement necessary to start an action potential.

Source by Jes B

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