No, there is a very fine line of difference between M-line and H-zone. M-line is defined as a fine line in the center of the A band of the sarcomere of striated muscle myofibrils, whereas the H-zone is the region of a striated muscle fibre that contains only thick myosin filaments. This region appears as a lighter band in the middle of the dark A band at the centre of a sarcomere. Though it is difficult to make out the differences between the M-line and H-zone very clearly, they are considered to be different populations.