Which of the following structures is contractile?

Tendons are classified as contractile structures because they connect muscles to bones and transmit the force generated by the muscles to facilitate movement. When a muscle contracts, the tendon pulls on the bone, enabling motion at the joint.

In contrast, skin, joint capsules, and cartilage do not have the ability to contract. Skin serves as a protective outer layer, joint capsules encase and stabilize joints, and cartilage provides cushioning and support within joints but does not contribute to active movement through contraction. The primary function of tendons in the musculoskeletal system is to facilitate movement by serving as a flexible yet strong connector between muscles and bones, which distinguishes them from the other structures listed.