What happens to a sarcomere during muscle contraction?

During muscle contraction, the sarcomere shortens. This is a fundamental feature of how muscle fibers generate force and movement. The sarcomere is the basic functional unit of muscle tissue, defined by the area between two Z lines. It contains filaments of myosin (thick filaments) and actin (thin filaments) that slide past one another during contraction.

When a muscle receives a signal to contract, the myosin heads attach to binding sites on the actin filaments, forming cross-bridges. As these myosin heads pivot, they pull the actin filaments closer together toward the center of the sarcomere. This sliding action decreases the length of the sarcomere without changing the length of the individual filaments themselves. As the sarcomeres shorten throughout the entire muscle, the muscle contracts and generates tension.

This process is known as the sliding filament theory of muscle contraction. Therefore, the correct answer highlights that the primary mechanical change occurring in a sarcomere during contraction is its shortening.