During muscle contraction, the length of all of the following reduce in length, except

During shortening of the muscle, i.e., contraction, the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length. 

The central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone. It also reduces due to the sliding of thin filaments into it.

Sarcomere is the distance between two Z-lines that hold the thin filaments. 

Both H-zone and sarcomere too reduce in length in contracted state.