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Skeletal Muscle Fiber Types
| Fiber type | Type I | Type IIa | Type IIX |
|---|---|---|---|
| Color | Red | Red | White |
| Contraction time | Slow | Moderate | Fast |
| Oxidative capacity | High | High | Medium |
| Mitochondrial density | High | High | Medium |
| Glycolytic capacity | Low | High | High |
| Resistance to fatigue | High | Intermediate | Lower |
| Major storage fuel | TAG | CP/glycogen | CP/glycogen |
| Capillary density | High | Intermediate | Low |
Abbreviation: CP, creatine phosphate, TAG, triglyceride.
