Question

Discuss red and white muscle fibres.

Answer 1

In mammals and birds, two types of skeletal muscle fibres, viz. (i) red, and (ii) white occur.

• Red muscle fibres (also called slow twitch fibres) are comparatively thin, darker in colour and slower in contraction rates.
  
• Their red colour is due to the presence (in the sarcoplasm) of a pigment called myoglobin.
  
• Mitochondria are more numerous in red fibres, but sarcoplasmic reticulum is less extensive.
• This sarcoplasm contains more glycogen. They can go on contracting for prolonged durations without fatigue.
  
• On the other hand, white muscle fibres (also called fast twitch fibres) are thicker, lighter in color, poorer in mitochondria, free of myoglobin and faster in contraction rates.
  
• Since the white fibres depend mainly on anaerobic glycolysis for energy production, they accumulate lactic acid in considerable amounts during strenuous work and soon get fatigued.