Fast contraction fibers, white or glycolytic : they predominate in the muscle used when it is necessary to develop great forces, they are fibers as their name indicates from fast, powerful and fast fatigue contractions, they predominate in athletes who compete in speed and strength activities short duration.
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- 2 Features
- 3 White fiber subtypes
- 4 Source
Low aerobic capacity
High glycolytic capacity (lactic acid)
Low capillary density
A great force of contraction
Wide distribution among athletes not engaged in endurance tests
- They are characterized by the abundance of myofibrils that occupy almost all of the sarcoplasm.
- The sarcoplasma is understaffed and its contents in mitochondria and myoglobin. It has a storage of carbohydrates in the form of glycogen.
- Anaerobic predominant metabolism due to the lack of mitochondria.
- More glycolytic enzymes for rapid energy release.
- They are large fibers for fast and powerful contractions.
- They need a large amount of calcium (Ca ++) and quick release.
- Develop movements where strength and speed intervene.
- They predominate in the upper limbs and even more so in the hands.
White fiber subtypes
Within the white fibers two types can be distinguished: Fibers II-A that obtain energy from both the aerobic and anaerobic routes through glycolysis and Fibers II-B in which only the anaerobic route practically exists . In this second case, both mitochondria and myoglobin are very scarce. Fibers II-B fatigue quickly because the amount of energyproduced is low, its reserves are low and the production of residual substances is high. Fibers II-A have an intermediate behavior regarding this characteristic. TYPE II – White fibers (Group B) They contain fewer myosin filaments, so they are much less vascularized. They accumulate very little carbohydrates and hardly accumulate lipids. They are indicated for short-time, high-intensity work. These types of fibers are the most used when working in the gym.