Question

What happens to the m line during muscle contraction?

Answer 1

I think the question is a little wrong it's not m line.However during muscle contraction the thin myofilaments move past the thick myofilaments due to which H-zone narrows.This reduces the length of I-band but retain the length of A-band.The Z-line attached to the action are also pulled inward causing the sarcomere to contract.

Answer 2

M line just helps in holding the thick filaments in 'A ' band together . During muscle contraction M line doesn't have any effect. It just helps to keep the filaments together and nothing else .