What best describes a muscle's role in movement?

A muscle's primary role in movement is to generate forces on joints, allowing the body to perform a variety of actions such as walking, running, lifting, and maintaining posture. Muscles contract and shorten, which pulls on tendons connected to bones, thereby creating the necessary force to move the skeletal system. This force is what enables different types of movements to occur, making them fundamental to any physical activity.

While other options may describe additional functions of muscles or the body's structure, they do not encapsulate the primary function of muscles related to movement as accurately as the generation of forces on joints does. For instance, limiting body movement and protecting internal organs pertain more to the roles of muscles as part of the broader structure and function of the body, rather than their direct contribution to movement itself. Storing energy is also a function of certain types of muscle tissue, such as storing glycogen in muscle cells, but it does not directly relate to the mechanics of movement. Therefore, the best description of a muscle's role in movement is indeed the generation of forces on joints.