Differences Between Type I and Type II Muscle Fibers

Key Concept: Mitochondrial Content

• Type I Muscle Fibers:

  • Mitochondrial Content: Higher
  • Color: Red (due to more mitochondria, which participate in oxidative phosphorylation)
  • Main Process: Oxidative Phosphorylation
  • Associated Molecules in Process: Oxygen (oxidation), Phosphate (phosphorylation)
  • Contraction Speed: Slow (energy production through mitochondria takes time)
  • Nerve Impulse Speed: Slow (termed "slow-twitch")
  • Activities: Aerobic (requires oxygen)
  • Duration of Contractions: Long (more energy available from mitochondria)
  • Fatigue Resistance: High (less likely to get fatigued)
  • Contraction Strength: Strong (more mitochondria, more energy, more muscle fibers contract)
  • Energy Storage: Triacylglycerides (fats)

• Type II Muscle Fibers:

  • Mitochondrial Content: Lower
  • Color: White
  • Main Process: Glycolysis
  • Contraction Speed: Fast (energy produced through glycolysis, which is quicker)
  • Nerve Impulse Speed: Fast (termed "fast-twitch")
  • Activities: Anaerobic (does not require oxygen)
  • Duration of Contractions: Short (less energy available)
  • Fatigue Resistance: Low (more likely to fatigue quickly)
  • Contraction Strength: Weak (less mitochondria, less energy, fewer muscle fibers contract)
  • Energy Storage: ATP, Creatine Phosphate (quick but short-lived energy sources)

Applications and Examples

• Type I Activities:

  • Postural support (e.g., standing for a long time)
  • Walking at a steady pace

• Type II Activities:

  • Quick, vigorous movements (e.g., shaking hands, snapping fingers)
  • Short bursts of activities that require strength (not for prolonged duration)

Summary

• Mitochondrial Content is the key determining factor between Type I and Type II muscle fibers.
• Type I fibers: slow-twitch, more mitochondria, aerobic, long-duration, less fatigue, strong contractions.
• Type II fibers: fast-twitch, less mitochondria, anaerobic, short-duration, quick to fatigue, weaker contractions.