During muscle contraction in humans, the:

Explanation

According to slidingfilament theory of muscle contraction, the actin and myosin filaments slide past each other with the help of crossbridge to reduce the length of the sarcomeres. The smallest unit of muscle contraction is a sarcomere (which is delineated by Zlines). As a muscle contracts, the Z lines come closer together (shortening sarcomere), the width of the I bands decreases, H -zone disappears ,but, there is no change in the width of the A band. During relaxation, crossbridges disappear and actin filaments slide back from Abands, the width of the I bands and H zones increases, but there is still no change in the width of the A band. A. Sarcomere does shorten. During contraction about 35% of sarcomere reduces in length. C. I bands shorten , H zone disappears but A bands donot change in length. D. Actin and myosin slide past each other but donot reduce.