Functional Capacity

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Functional capacity refers to the capability of performing tasks and activities that people find necessary or desirable in their lives. One way of examining the effects of disease on people and communities is through mortality and morbidity (illness) statistics. But another way, which took on increased significance in the last decades of the twentieth century, is through examining functional status or functional capacity. Whereas mortality and morbidity tends to be examined relative to specific diseases or conditions, functional capacity tends to be considered over and above the various combinations of diseases a person has that might contribute to functional difficulties.

Functional capability is most appropriately examined with reference to particular life-cycle tasks that an individual may need to perform. For children, functional requirements include learning at school, participating in play, and involvement in family life. For adults, functional abilities in the labor force are important, as well as (in many cases), activities related to rearing and inter-acting with their children. Some assessment tools examine the ability to perform such age-related tasks in some detail. Other assessment tools, especially those used in large-scale research, attempt to use questions that work for all age groups. An example of a general questions about functional capacity would be: "How often are you unable to perform your usual activities because of illness or disability?" This approach would be less than optimal for persons of retirement age, who may not have a wide range of "usual activities." A narrower, more general approach is to ask how many days an individual has been in bed because of illness or disability in a particular time period. The most common approach is to consider ability to perform each in a list of specific tasks or activities.

Functional capacity measures have particularly been emphasized for people who need long-term care, which disproportionately includes elderly people. In fact, the need for long-term care services, as well as eligibility for services under public funding or insurance programs, tends to be measured by an individual's inability to perform various functional activities. With reference to older people and others needing long-term care, two common terms have emerged to characterize functional capacity: ability to perform "activities of daily living" (ADLs) and ability to perform "instrumental activities of daily living" (IADLs).

ADLs are the most basic of self-care functions. In the 1960s, Dr. Sydney Katz evolved the art of ADL measurement based on his work in the rehabilitation of people with hip fractures and strokes. He developed a simple measure that classified people as independent or dependent on each of six ADL functions: bathing, dressing, using the toilet, transferring in and out of beds or chairs, continence, and eating (continence is now usually removed from ADL measures because it is more indicative of a physiological state than a function). When ADL is measured dichotomously, people are usually considered independent if they can do the function without help (even if they depend on equipment) and dependent if they need human help. Depending on the level of detail sought, some ADL measures use a more graduated scale to measure degrees of dependency; some break down the tasks (e.g., dressing can include upper body, lower body, putting on shoes); and some add tasks (e.g., walking a certain number of feet, climbing stairs). IADLs are functions that may be needed for independence depending on task allocation in a family unit and demands made by a person's life. They include cooking, cleaning, laundry, shopping, making and receiving telephone calls, driving or using public transportation, and taking medicines.

Lack of functional capacity in each ADL or IADL task can result from any combination of physical problems, memory loss, lack of social resources, or lack of motivation (e.g., because of depression). Thus, when trying to improve someone's functional ability in, say, cooking, one could attempt to change any of these parameters. If memory loss is the reason for functional impairment, some people might be able to perform the function with cueing and reminders. Sometimes people become more functional when a task is simplified. Sometimes physical rehabilitation or provision of a wide range of prosthetic aides (dentures, hearing aides, canes, or specialized equipment) improves functional abilities. The variation in the amount of human help needed to become functional on any given task can be considerable, ranging from just stand-by assistance for safety to the physical help of two or more people.

Functional capability can be measured by questions about what a person can do, or by demonstrations of actual ability (e.g., getting up from a chair, demonstrating ability to hold food on a spoon and bring it to one's mouth, opening a medicine bottle and taking out the correct number of pills). It can also be measured by questions about what a person actually does do. The measurement strategy should be tailored to the purpose of getting the information. Rehabilitation programs need to know about capacity, and often in considerable detail. For program evaluation and quality assurance, actual functioning may be more important than capacity. For example, a person may be capable of bathing without help, but may never do it because of rules in the nursing home in which he or she resides. Some would argue that the actual independence exercised is what matters in terms of quality of life.

Rosalie A. Kane

(see also: Geriatrics; Gerontology; Health; Health Measurement Scales; Health Outcomes; Quality of Life )


Applegate, W. B.; Blass, J. P.; and Williams, T. E. (1990). "Instruments for the Functional Assessment of Older Patients." New England Journal of Medicine 322(17): 11321148.

Kane, R. L., and Kane, R. A. (2000). Assessing Older Persons: Measurement, Meaning, and Practical Applications. New York: Oxford University Press.

McDowell, I., and Newell, C. (1996). Measuring Health: A Guide to Rating Scales and Questionnaires, 2nd edition. New York: Oxford University Press.