When a skeletal muscle contracts which which bands change in size and why?

When a skeletal muscle contracts, the I bands and H zones decrease in size, while the A band remains constant. This occurs because the thin filaments (actin) slide past the thick filaments (myosin) during contraction, causing the sarcomeres to shorten. As the sarcomeres contract, the overlapping of filaments increases, leading to a reduction in the I band and H zone, while the length of the A band is preserved since it represents the length of the thick filaments.