The most common source of activity limitation in early adulthood is

Arthritis

Arthritis is a joint disorder in which there is inflammation of one or more joints. Arthritis is frequently accompanied by joint pain. There are many types of arthritis and over 100 have been identified. The causes of arthritis include injury, metabolic abnormalities, hereditary factors, effect of infections, and a misdirected immune system. Arthritis is mostly common among women and occurs as people get older. Severe arthritis can result in chronic pain, inability to do daily activities and can cause difficulty in walking.