Skeletal Muscle Fibres
Skeletal muscles are composed of fibers that have markedly different morphological and physiological characteristics. These differences have led to several different systems of classification, based on a variety of criteria. The most familiar approach is to classify fibers according to twitch time, employing the terms slowtwitch and fast-twitch fiber. Because a motor unit is composed of muscle fibers that are all of the same type, it also can be designated using this classification system. A fast-twitch motor unit is one that develops force and also relaxes rapidly and thus has a short twitch time. Slow-twitch motor units, in contrast, develop force and relax slowly and have a long twitch time.
TYPES
- TYPE I (SLOW-TWITCH)
- TYPE IIA (FAST-TWITCH / INTERMEDIATE)
- TYPE IIB (FAST-TWITCH)
| Characteristics | TYPE I | TYPE IIA | TYPE IIB/X |
| Motor neuron size | Small | Large | Large |
| Recruitment threshold | Low | Intermediate/High | High |
| Nerve conduction velocity | Slow | Fast | Fast |
| Contraction speed | Slow | Fast | Fast |
| Relaxation speed | Slow | Fast | Fast |
| Fatigue resistance | High | Intermediate/Low | Low |
| Endurance | High | Intermediate/Low | Low |
| Force production | Low | Intermediate | High |
| Power output | Low | Intermediate/High | High |
| Aerobic enzyme content | High | Intermediate/Low | Low |
| Anaerobic enzyme content | Low | High | High |
| Sarcoplasmic reticulum complexity | Low | Intermediate/High | High |
| Capillary density | High | Intermediate | Low |
| Myoglobin content | High | Low | Low |
| Mitochondrial size, density | High | Intermediate | Low |
| Fiber diameter | Small | Intermediate | Large |
| Color | Red | White/Red | White |
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References
- Essentials of strength training and conditioning., 4th edition.
Creator Details
| Name | : | Deva senathipathi |
| Qualifications | : | Physiotherapist |
