Answer:
Cross-bridges
Explanation:
A Sarcomere is the functional unit of the muscle which is composed of the myofilaments called the actin and myosin.
The actin and myosin filaments when form cross bridge that is a structure formed when the myosin binds the actin is responsible for the muscle contraction and relaxation. The muscle contracts when a power stroke is experienced after the cross-bridge formation.
The sarcomere length shortens up to 75 to 130 per cent of its normal length during contraction as the maximum number of the cross-bridges are formed between this range and cause the repeated power stroke.
Thus, cross-bridge is the correct answer.
