“Activity limitations” is defined in WHO ICF as limitations in mobility or self-care. Examples of activity limitations are inability to walk, problems learning, difficulty toileting, restricted social abilities, or trouble communicating [13]. These may or may not be able to be ameliorated through the use of assistive device or environmental modifications.

The term “participation restriction” has replaced “handicap” in terms of life activities and roles such as attending school, maintaining gainful employment, or pursuing relationships. The previous concept was that the handicap resided in the person (“the person is handicapped”), but the new model emphasizes the role of the social and physical environments in either restricting or enabling participation (“the person needs accommodations to get to work”). Thus, participation restrictions can include problems in school or work or difficulty with mobility.

The term “disability” refers to both activity limitations and participation restrictions. For example, an individual with a missing digit may have impairment, but no disability. Individuals with amputation may have equal impairment and disability. Individuals with craniofacial abnormalities may have little impairment but great disability due to others’ reactions.

The WHO ICF also includes additional “contextual factors” that influence functioning of the individual. “Environmental factors” are the external elements which affect the experience of the individual, including technology, attitudes, and services. Environmental factors that could enable activity and participation are assistive devices and technology, personal care attendants, physical modifications to the environment, policy or legal protections, or inclusive social atmospheres. In contrast, certain environmental factors could impede the individual, including the presence of abuse, inaccessible architectural structures, cold weather and rough terrain, and inflexible work environments. “Personal factors” can include intersecting elements such as gender identity, age, sexual orientation, socioeconomic status, education level, personality characteristics, and other identities that influence the experience of disability, such as important life events and developmental stages.

The WHO ICF model can be applied to a wide range of health conditions and disabilities. Sometimes impairment does not result in any functional limitations. An injury may not necessarily lead to impairment. Environmental factors can affect activity limitations. The dynamic nature of impairments and activity limitations are better reflected in this model than in more simplistic conceptualizations. Table 9.1 includes WHO ICF examples of the interface among health conditions, impairments, activity limitations, and participation restrictions, highlighting how environmental factors mediate functioning.