Osteoarthritis is a chronic disease of the joint cartilage and bone, often thought to result from "wear and tear" on a joint, although there are other causes such as congenital defects, trauma and metabolic disorders. Joints appear larger, are stiff and painful and usually feel worse the more they are used throughout the day.

Osteoarthritis is associated with the aging process and can affect any joint. The cartilage of the affected joint is gradually worn down, eventually causing bone to rub against bone. Bony spurs develop on the unprotected bones causing pain and inflammation.

Osteoporosis is a condition characterized by progressive loss of bone density, thinning of bone tissue and increased vulnerability to fractures. Osteoporosis may result from disease, dietary or hormonal deficiency or advanced age. Regular exercise and vitamin and mineral supplements can reduce and even reverse loss of bone density.

Flexibility exercise in its simplest form stretches and elongates muscles. Disciplines which incorporate stretching with breath control and meditation include yoga and t'ai chi. The benefits of greater flexibility may go beyond the physical to the improvement of stress reduction and the promotion of a greater sense of well-being.

Joints, particularly hinge joints like the elbow and the knee, are complex structures made up of bone, muscles, synovium, cartilage, and ligaments that are designed to bear weight and move the body through space. The knee consists of the femur (thigh bone) above, and the tibia (shin bone) and fibula below. The kneecap (patella) glides through a shallow groove on the front part of the lower thigh bone. Ligaments and tendons connect the three bones of the knee, which are contained in the joint capsule (synovium) and are cushioned by cartilage.