MUSCLE WORK MAKES THE DREAM WORK...
As part of it principles structure, skeletal muscles are arranged in groups of muscle fibers. Each group of muscle fibers is surrounded by fascia, then several groups of muscle fibers are groups together into an even bigger group via fascia, and so on and so forth, until the entire skeletal muscle is built. This is of course a simplification of a skeletal muscle's structure.
Every skeletal muscle is made up of a certain combination of three skeletal muscle fibers types. There are several ways to distinct and address the skeletal muscle fiber types, each one method of describing the fibers emphasizes a different major characteristic of the fibers as the basis for distinction. Very commonly (in an unprofessional way), the fibers are described according to their color: "red" muscle fibers, "pink" muscle fibers, and "white" muscle fibers. the difference in color is a visual effect caused by the extent of oxygen content within the muscle fibers.
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As a matter of principle, the greater the oxygen content of a tissue (any tissue), the more red the tissue seems in color.The less oxygen within the tissue, the more pink or white that tissue will look visually. Accordingly, a "red" muscle fiber would indicate greater oxygen content and a more aerobic function implied therefor. the "pink" muscle fiber implies some oxygen content within the fiber, yet less than the "red" fiber. This means that these fibers have some aerobic capacity, yet not as much as the "red" fiber.
The third fiber is the "white" fiber, which would suggest very little to no oxygen content within the fiber. The less oxygen a muscle fiber has, the more anaerobic the function of the fibers becomes. Indeed, out of the three muscle fiber types, two are considered mainly anaerobic, and the third muscle fiber type is considered mainly aerobic.
The more physiological way of creating distinction between the fibers is to analyze how fast or slow they produce muscle force, and how fast or slow they experience fatigue. Accordingly, the three muscle fiber types are called STRF, FTRF, and FTF. STRF stands for Slow Twitch, Resistance to Fatigue. Twitch represents the neural process required to stimulate the muscle fibers to produce force, while resistance to fatigue represents the tendency of the fibers to get tired. The more resistance to fatigue a muscle fiber has, the slower it gets fatigued.
Accordingly, the STRF muscle fiber is the most aerobic muscle fibers. Since it produces its energy aerobically, it produces its energy the slowest, and gets fatigued slower as aerobic metabolism creates lesser extents of fatigue (on a relative scale). FTRF stand for Fast Twitch, resistance to Fatigue. Thus, this muscle fiber develops its force fast because it is mainly an anaerobic muscle fiber, yet has a low-medium ability to create energy aerobically, thus has some resistance to getting fatigue.
FTF stand for Fast Twitch, Fatigue. Thus, this muscle fiber develops its force fast, yet gets fatigued extremely fast (very low resistance to fatigue). This muscle fiber has a very low oxygen content, and thus low aerobic energy production capacity. It is an anaerobic muscle fiber. In comparison, the STRF fiber is the most aerobic of all, produces energy efficiently, the slowest of all to produce its force, yet is slowest to get tired; FTRF fibers are not the middle between STRF and FTF fibers, they are mostly anaerobic in nature, yet have sone aerobic capacity. They do not have as much aerobic capacity as the STRf fibers, and do not develop as much force as the FTF fibers, nor as fast.
FTF fibers are the most anaerobic, they develop the force the fastest of all, and the most force of all, yet they cannot sustain activity for long, since they fatigue fastest. STRF fibers are activated the most during aerobic activities of 120 seconds or more; FTRF fibers are activated the most in activities of 30-120 seconds; and FTF fibers are activated the most during activities that are 1-30 seconds long.
Accordingly, STRF fibers are used for aerobic power and aerobic endurance activities; FTRF fibers are used for muscular (anaerobic) endurance activities; FTF fibers are used the most in muscular (anaerobic) power activities, also known as "explosive power" or "explosive movements" that demand maximal muscle strength in minimal time to force production.
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Last but not least, we distinct the muscle fiber according to their type. Type I muscle fibers are the STRF fibers, the aerobic muscle fiber type. Type IIa muscle fibers are the FTRF fibers, one out of two anaerobic muscle fibers. Type IIx muscle fibers are the FTF fibers, the other anaerobic muscle fiber type.
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