| Type I (slow twitch) | Type II (fast twitch) | |
|---|---|---|
| Action | Sustained force (e.g., posture) | Rapid bursts (e.g., heavy weightlifting) |
| Activity type | Endurance (aerobic) | Resistance (anaerobic) |
| Force generated | Low | High |
| Resistance to fatigue | High | Low |
| Lipid content | High | Low |
| Glycogen content | Low | High |
| Mitochondrial content | High | Low |
| Energy metabolism | Oxidative | Glycolytic |
| Color | Red (high myoglobin) | Pale red/white (low myoglobin) |
| Prototype | Soleus muscle of the lower leg and paraspinal muscles of the back | Triceps |
Mnemonic
“Too (2) fast to last; light and white, no air to spare.” The most important features of type 2 skeletal muscle fibers are fast-twitching, short-term activity, white appearance, and anaerobic glycolysis (no air).