During the contraction of a skeletal muscle, which of the following does NOT change in length?

Explanation

The A band is the full length of the thick myosin filaments, and since the filaments themselves do not shorten, the A band stays the same width throughout contraction. The I band and the H zone both narrow because the thin filaments are pulled inwards over the thick ones, and the sarcomere as a whole therefore shortens. This constant A band is the strongest single piece of evidence for the sliding filament model.