Explain how it is that actin and myosin in the sarcomere never actually shorten and yet the muscle as a whole does?

Actin and myosin are proteins in the sarcomere that interact through a process called the sliding filament mechanism. During muscle contraction, myosin heads attach to actin filaments and pull them closer together, but the lengths of the filaments themselves do not change. Instead, the sarcomere shortens as the actin filaments slide over the myosin filaments, resulting in the overall shortening of the muscle fiber. This coordinated action across many sarcomeres leads to the contraction of the entire muscle.