Those who are new to bodybuilding have a vague impression about their muscles as a mass of sinewy material that is similar wherever it is found in the body. The fact is that there are several different muscle fibers types and each type responds differently to training. Of course you can’t perceive the differences looking at the human body from the outside, but physicians and other healthcare professionals that are involved in the field, do clearly understand the differences. A brief description of each main muscle fiber type is discussed below.
Type A Fast-twitch Muscle Fibers
Type A fast-twitch muscle fibers are those responsible for the heavy work of the body. As a result, they also get tired the quickest. These are the types of muscle fiber that are working the hardest during a bench press set. They have very large motor neurons and an extremely low mitochondrial density. They also do not utilize oxygen very efficiently, explaining why they come up short on endurance. Oxygen must be present in these muscles to support the contractions. These muscles rely upon creatine phosphate and glucose for energy. They do not use or benefit from stored body fat, because they can contract continually for only about twenty seconds.
Type B Fast-twitch Muscle Fibers
Type B fast-twitch muscle fibers are come into play during activities of short duration. Sprinters use mostly Type B in their short but intense bursts of speed. Type B has large motor neurons similar to the Type A fibers. Their resistance to fatigue in intermediate and they have a very high mitochondrial density. These types of muscle fiber are far more efficient in the use of oxygen than the Type A muscle fibers, and consequently have a much higher resistance to fatigue and the ability to contract for longer periods of time.
Slow-twitch Muscle Fibers
Slow-twitch muscle fibers are used for activities of extended duration, such as long distance running and other similar medium-to-low intensity activities. These muscle fiber types are evolved to resist fatigue and hand oxygen very efficiently. Characteristically, they are relative slow to contract and do not generate a significant amount of force. They are known for their endurance more than for their power. Their mitochondrial density is very high and they have a large number of capillaries that permits the muscles to use oxygen with great efficiency, enabling the muscles to handle work for extended periods of time. Unlike the Type A and Type B muscle fibers; these muscles use fat as fuel in addition to carbohydrates and creatine phosphate.
Training the Different Muscle Fiber Types
Each of the different types of muscle fiber requires slightly different training protocols.
Because the Type A muscle fibers are the primary force generators, exercises directed to developing these muscles should be those that exert maximum effort over a short period of time, such as running for a short distance at top speed, lifting one to five repetitions lifting, and any suitable plyometric exercise.
Type B muscle fibers types should be exercised with less force that Type A, but over a slightly longer period of time. An example would be to perform thirty to forty intervals repeated ten times for about one minute at a moderate pace. An example of weight training would be to work in the six to ten repetitions range to take advantage of the higher oxidation ability of these muscles. These muscles are used in endurance activities, and therefore require longer training periods to effectively challenge them into growth. If you run, run longer. If you bicycle, travel farther. If you swim, swim farther.
When you reevaluate you training and workout regimen, consider the differences among these muscle fibers types and adjust your training to effectively address their differences.
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