According to the sliding filament theory,

According to the sliding fi lament theory, during muscle contraction, the actin and myosin filaments slide over each other. I band and H zone shorten. However, the length of the A-band remains constant during muscle contraction. 

(1) During muscle contraction, the actin and myosin filaments slide over each other, causing the sarcomere to shorten.
Sarcomere does not increase in length. 

(3) The I-band is the region of the sarcomere containing only actin filaments. During muscle contraction, as the actin filaments slide closer to the center of the sarcomere by overlapping with the myosin filaments, the I-band becomes shorter.

(4) The actin filaments do not slide away from the A-band during muscle contraction. The actin filaments slide toward the center of the sarcomere, overlapping the myosin filaments, and this sliding action shortens the sarcomere.