When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap completely.
Cut Rita Zahara
“The Sliding Filament Model of Muscle Contraction ,” Open Educational Resource (OER) - UNM, accessed February 25, 2020, http://oer.unm.ac.id/items/show/1127.