Table 1.
Skeletal muscle fiber types and their properties.
| Myofiber type/properties | Type 1 | Type 2a | Type 2b | Type 2x/d |
|---|---|---|---|---|
| Myosin heavy chain isoform | MyHC1 | MyHC2a | MyHC2b | MyHC2x/d |
| myofiber cross-sectional area | Small | Intermediate | Large | Large |
| Myosin ATPase activity | Slow | Fast | Fast | Fast |
| Energy metabolism | Oxidative | Predominantly oxidative | Glycolytic | Glycolytic |
| Twitch | Slow | Moderate | Very fast | Fast |
| Fatigue | Resistant | Moderately resistant | Fast fatigue | Fast fatigue |
| Force production | Weak | Intermediate | Very high | Strong |
| Endurance capacity | High | Intermediate | Low | Low |
| Myoglobin content | High | High | Low | Low |
| Appearance | Red | Red | White | White |
| Mitochondria numbers | High | High | Low | Low |