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. Author manuscript; available in PMC: 2011 Apr 5.
Published in final edited form as: PM R. 2010 Nov;2(11):1035–1045. doi: 10.1016/j.pmrj.2010.06.013

Table 1.

The hierarchies of functioning: the medical model, the social model, and the ICF taxonomy

Levels* Medical Model
Terminology, Examples,
and Concepts		 Social Model Terminology
and Concepts		 ICF Terminology†
Level 1 (molecular or cellular) Genetic predisposition, pathology, cellular injury, allostatic load, subclinical cellular dysregulation NA NA
Level 2 (body tissue) Diagnosis of illness or injury (mental/physical, morbidity) NA “In the context of health”
Level 3 (organ or system) Physical impairment, functional limitation, reduced reserve, cognitive impairment, organ or system-level dysregulation Aspects of a person’s mind or body that do not function normally (including lack of motivation, initiative, engagement) Body functions are the “physiological functions of body systems, including psychological functions”
Body structures are “anatomical parts of the body such as organs, limbs and their components”
Impairments are “problems in body function or structure such as significant deviation or loss”
Level 4 (whole organism or individual person) Frailty at the organism level, disability, reduced resiliency or energy, inability to perform ADLs/IADLs at the organism level Disability as a disadvantage Activity is the “execution of a task or action by an individual”
Activity limitations are “difficulties an individual may have in executing activities”
Participation is “involvement in a life situation”
Participation restrictions are “problems an individual may experience in involvement in life situations”
Level 5 (environmental experience) Pathogens and hazards in the environment Barriers, loss, or limitation of opportunities resulting from direct or indirect discrimination Social and physical environmental barriers and facilitators

ADL = activities of daily living; IADL = instrumental activities of daily living; ICF = International Classification of Functioning Disability and Health; NA = not applicable.

*

Functional level 1 applies basic science in efforts to understand and improve medical and surgical management of levels 2 and 3. Levels 3 and 4 are the primary focus of physical medicine and rehabilitation, and level 5 needs development and exploration.

†

From World Health Organization. International Classification of Functioning, Disability and Health: ICF. Geneva, Switzerland: World Health Organization; 2001 (pages 3 and 10).