Which skeletal muscle band does NOT shorten during muscle contraction?

The A band does not shorten during muscle contraction because it contains the thick filaments (myosin) which maintain their length throughout the contraction process. The A band is defined by the entire length of the thick filaments, irrespective of the degree of overlap with the thin filaments (actin) during contraction.

As the muscle contracts, the actin filaments slide over the myosin filaments, leading to a reduction in the lengths of the I band and H band. However, since the A band corresponds to the region of the thick filaments that does not change in length, it remains constant.

In contrast, the I band and H band will shorten due to the sliding filament mechanism, where the actin filaments slide into the region occupied by the thick filaments, while the Z lines move closer together, affecting these regions specifically. Hence, it is the A band that maintains its length throughout contraction, which is why it is the correct answer to the question.