Final answer:
During muscle fiber shortening, the thin and thick filaments slide past each other in the sarcomere, causing the muscle to contract.
Step-by-step explanation:
During muscle fiber shortening, the thin and thick filaments slide past each other. The sarcomere, which is the unit of contraction in a muscle cell, shortens as the filaments slide, causing the muscle to contract. However, it is important to note that the filaments themselves do not change in length.