Final answer:
The A band remains constant in width during muscle contraction, true to the Sliding Filament Model. The I band decreases and the Z lines move closer, but the A band's length remains unchanged.
Step-by-step explanation:
The statement that the A band remains constant during muscle contraction is True. During muscle contraction, as per the Sliding Filament Model, the Z lines move closer together and the I band gets smaller. However, the A band, which comprises the length of the thick filaments within the sarcomere, maintains its width even at full contraction when the thin and thick filaments overlap completely. The shortening of the H zone and the closer proximity of the A bands of different sarcomeres contribute to the muscle contraction, but the A band itself does not shorten.