- A The A band shortens noticeably while the I band stays mostly unchanged throughout contraction
- B I band and H zone decrease; A band stays same; Z discs come closer together
- C All visible bands of the sarcomere shorten by a roughly equal amount during contraction
- D Mainly the H zone changes noticeably, with little movement of the Z discs
Correct answer: B. I band and H zone decrease; A band stays same; Z discs come closer together
Explanation: During contraction: I band (thin filaments only) decreases; H zone (thick filaments only) decreases; A band (thick filaments throughout) stays the SAME length; Z discs move closer together. This is because filaments slide but do not shorten.
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.