Classification of human skeletal muscle fibres and distinctive functional or molecular properties of each fibre type
| SR, sarcoplasmic reticulum. | |||
| Classifications: | |||
| Myosin based classification | Slow or type 1 | Fast 2A | Fast 2X |
| Classification based on metabolism and time course | Slow oxidative (SO) | Fast oxidative (FOG) | Fast glycolytic (FG) |
| Classification based on fatigue resistance | Slow fatigue resistant (S) | Fast fatigue resistant (FFR) | Fast fatiguable (FF) |
| Properties: | |||
| Myosin isoforms | 1 or slow | Fast 2A | Fast 2X |
| Maximum shortening velocity | Slow | Fast | Very fast |
| Myofibrillar ATPase activity | Low | High | Very high |
| Calcium uptake in the SR | Slow | Fast | Fast |
| Time course of the twitch | Slow | Fast | Fast |
| Resistance to fatigue | High | Intermediate | Low |
| Metabolism | Oxidative | Oxidative glycolytic | Glycolytic |