- A Red muscle fibres are sometimes mistakenly classified as fast-twitch while white fibres are instead mistakenly classified as slow-twitch in most textbook accounts
- B Red fibres (high myoglobin, slow-twitch, aerobic) appear red due to high myoglobin content; white fibres (low myoglobin, fast-twitch, anaerobic) appear pale
- C Both of these fibre types are sometimes thought to contain a roughly equal concentration of the oxygen-binding protein myoglobin in their cytoplasm during normal conditions
- D White muscle fibres are sometimes mistakenly thought to be the single most predominant fibre type found distributed throughout the entire heart wall as generally observed
Correct answer: B. Red fibres (high myoglobin, slow-twitch, aerobic) appear red due to high myoglobin content; white fibres (low myoglobin, fast-twitch, anaerobic) appear pale
Explanation: Myoglobin stores oxygen in muscle. Red (slow-twitch, Type I): high myoglobin, many mitochondria, aerobic respiration, fatigue-resistant. White (fast-twitch, Type II): low myoglobin, fewer mitochondria, anaerobic glycolysis, fast but fatigue quickly. Poultry: breast (white, fast - flight bursts), legs (red, slow - standing/walking).
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.