Impairment, disability and handicap are all related to conditions that make it hard or impossible for an individual to function in a normal capacity and the effect of those conditions. An impairment is the abnormality itself, and a disability is the restriction that is caused by the abnormality. A handicap is the manner in which the impairment restricts the normal functioning of an individual.
An impairment occurs when there is a problem that affects the normal human body structure or organ. An example of an impairment is someone who has cerebral palsy, because it affects the structure of the body of those who suffer from it in several ways. It causes the joints to stiffen due to painful contractions in the muscles, which make it hard for the individual to move the various limbs. It also causes the jaws to contract and clench together in a manner that makes it a struggle for some individuals to unclench the jaw. Cerebral palsy also leads to stunted growth and deformity of the limbs in some individuals. All of these factors affect the physical structure of the body and are included in the definition of an impairment.
Disability refers to the way in which the impairment restricts the movements and activities of the individual. In the case of the individual with cerebral palsy, the impairment may affect the ability of the individual to walk. This is due to the fact that the individual cannot coordinate the twisted and stiff muscles to use them to walk. In severe cases of cerebral palsy, the individual may be unable to move at all due to damage in the brain and the resulting disconnect between the cognitive faculty necessary to learn how to function and the ability to control the limbs for movement. In relatively milder cases of cerebral palsy in which the individual retains full or partial cognitive faculties, such an individual might be able to learn how to move about using movement aids. The use of such aids reduces the level of the disability.
In this situation, the handicap stems from the extent of restriction that the impairment and disability impose on the individual. The criteria for measuring the handicap is by assessing how other normal people in such a situation would cope. As such, those who have cerebral palsy are handicapped in the sense that they cannot do things common to people in their age group and environment. For instance, if the individual who has cerebral palsy is eight years old, he or she is handicapped to the extent that he or she cannot play with children in the same age group, and in some cases, cannot even do everyday tasks like feeding him or herself.