• Joints are the junctions that link bones together. The architecture of each joint — that is, whether its structure is a hinge, pivot, or ball-in-socket — determines how the bones can move.
• Tendons are flexible cords of strong tissue that connect muscles to bones.
• Ligaments are tough, fibrous bands of tissue that bind bone to bone, or bone to cartilage, at a joint. An example is the anterior cruciate ligament (ACL), one of five ligaments that together control the movements of the knee. Among other things, the ACL keeps the knee joint from rotating too far.

When you stretch, you’re working muscles and tendons rather than ligaments. Ligaments are not supposed to be elastic. An overly stretchy ligament wouldn’t provide the stability and support needed for a safe range of movement.