What happens during contraction according to the sliding filament theory?

During contraction, according to the sliding filament theory, actin filaments slide over myosin filaments, which results in the sarcomere, the basic unit of muscle fiber, becoming shorter. This sliding action pulls the ends of the sarcomere together, leading to muscle contraction.

The interaction between actin and myosin involves the binding of myosin heads to actin, forming cross-bridges. When the myosin heads pivot, they pull the actin filaments towards the center of the sarcomere, which causes the muscle to contract. This process is fundamental to how muscles generate force and movement in the body.

The other options describe processes that do not coincide with the mechanism of contraction defined by the sliding filament theory, such as relaxation or alterations in muscle fiber integrity. Thus, the correct understanding is firmly rooted in the sliding interaction of actin and myosin during muscle contraction.