Ligaments are the fibrous, slightly stretchy connective tissues that hold one bone to another in the body, forming a joint. Ligaments control the range of motion of a joint, preventing your elbow from bending backwards, for example, and stabilizing the joint so that the bones move in the proper alignment.

Ligaments are composed of strands of collagen fibers. While ligaments are slightly stretchy, that they are arranged in crossing patterns prevents the joint itself to become loose.

Stretching exercises increase the length and flexibility of the muscles, allowing the joint to move farther than before. The ligaments themselves are not stretched, as they provide the support for the joint. This stretching of the muscles is what allows martial artists to perform seemingly impossible kicks and contortionists to stretch their bodies into fantastic positions.

If ligaments are stretched, either by injury, excess strain on a joint, or by improper stretching techniques, the joint will become weaker, as the elongated ligaments are unable to properly support it. People who are said to be "double jointed" simply have extra long ligaments that allow their joints to stretch beyond the normal range.

Because ligaments are so important in the stabilization of joints, they are also highly susceptible to injury. The anterior cruciate ligament located behind the knee, often referred to as the ACL, is commonly damaged in rough sports.

Because connective tissue such as ligaments must withstand a great deal of stress in day to day activities and have a relatively low blood supply, injuries can take a very long time to heal, and sometimes require surgery. Many professional athletes have had multiple surgeries to ligaments over the course of their careers.

Severe injury to ligaments can often require physical therapy. Even with surgery and physical therapy, injured ligaments tend to be less flexible, and more prone to repeat injury, so patients should be careful when engaging in strenuous activities that can put excess pressure on the injured ligaments.