7.9—Movement by muscles, tendons, skeleton and ligaments

Muscles generate pulling force; bones resist bending and act as levers. Tendons connect muscle to bone and transmit force, while ligaments connect bone to bone and stabilise joints.

Because a muscle cannot push, opposing muscles work antagonistically around a joint. One contracts while its partner relaxes to reverse the movement.

To flex the elbow, biceps contract and triceps relax; to extend it, triceps contract and biceps relax. The bone provides the rigid structure being pulled.

Tendons are not ligaments, and a relaxed antagonist is not necessarily inactive in every movement. Identify the joint action and force direction.