Cartilage is a smooth, flexible connective tissue that is in the skeletal systems of animals (including both sharks and humans) that is more rigid than muscle but less rigid than bone. In cartilaginous fish, like sharks, the entire skeleton is composed of cartilage. Humans, in contrast, have bone-based skeletal systems. Some people recommend taking shark cartilage supplements to treat certain illnesses, including cancers and arthritis, but the effective of these treatments are not supported by scientific evidence.

Tendons attach muscle to bone, while ligaments attach bone to bone. Both tendons and ligaments are made of collagen. Tendons work with muscles to move bone, while ligament usually serves to hold structures together and keep them stable. Tendons and ligaments are both made of collagen fibers, however, in tendons the fibers are parallel and in ligaments they criss-cross, helping them to perform their respective purposes. Both tendons and ligaments are often injured in sports players. A very common ligament injury for athletes is the tearing of the anterior cruciate ligament (ACL), which is found in the knee and is necessary for stability. Tendonitis is a very common problem for athletes as well, in particular, tendonitis of the Achilles tendon (which connects the heel to the lower leg muscle).