Functional limitations are useful to assess because they are often strong predictors of clinically meaningful, distal outcomes, such as disability, nursing home admission, and death. Increasingly, however, assessments of functional limitations have been included in longitudinal studies and clinical trials as more proximal outcomes. In contrast to measures of disability, measures of functional limitations are usually free of environmental influences, often focus on a specific task, such as gait speed, thereby leading to greater specificity, and offer the potential for greater responsiveness to clinically meaningful changes.
Functional limitations are assessed most commonly with tests of physical performance, in which an individual is asked to perform a specific task (or series of tasks) and is evaluated in an objective, standardized manner using predetermined criteria, which may include counting of repetitions or timing of the activity as appropriate.
One of the most widely used and validated assessment tools is the Short Physical Performance Battery (SPPB), which was originally developed at the National Institute on Aging for use in the Established Population for the Epidemiologic Studies of the Elderly (EPESE) (8
). The SPPB, which assesses lower extremity functional limitations, includes timed tests of standing balance, walking speed, and repeated chair stands. For the balance test, persons are asked to maintain their feet in side-by-side, semi-tandem (heel of one foot beside the big toe of the other foot), and tandem (heel of one foot in front and touching the other foot) positions for 10 seconds each. Walking speed is assessed by asking persons to walk at their usual pace over a 4-meter course. Two walk times are recorded and the faster of the two is used to compute the walking test score. For the chair stand test, persons are asked to stand up from a sitting position with their arms folded across their chest. If able to perform this task, they are then asked to stand up and sit down five times as quickly as possible and the time to perform the test is recorded. Each of the three tests is assigned a score ranging from 0 to 4, with 0 indicating the inability to complete the test and 4 the highest level of performance. A summary score, ranging from 0 to 12, is calculated by adding the three scores. The SPPB usually takes less than 10 minutes to complete and is portable, allowing it to be completed in the home or office. The test-retest reliability of the SPPB and each of its components is high (9
). The SPPB is available for use without permission or royalty fees; and the contents of a training CD, including comprehensive instructions on the administration of the battery, safety tips, a scoring sheet and background information on relevant publications, can be downloaded from www.grc.nia.nih.gov/branches/ledb/sppb/index.htm
The SPPB is a strong predictor of mortality, nursing home admissions, and the onset of disability in activities of daily living and mobility, respectively (8
). Although these associations are largely linear, with outcome rates increasing as scores on the SPPB decrease, an SPPB score less than 10 has commonly been used to identify an “at risk” group. Older persons having scores from 10 to 12 are relatively immune to adverse outcomes over the course of four years. In addition, the SPPB is responsive to clinically meaningful changes (9
), with 0.5 points denoting a small change (i.e. clinically detectable, potentially important) and 1 point denoting a substantial change (clinically detectable, definitely important) () (12
Criteria for Responsiveness*
Although each of its three components is valid (8
), the predictive accuracy of the SPPB is due largely to gait speed (13
). As the single best indicator of functional limitations, slow gait speed has been used to identify older persons who are physically frail in longitudinal studies and clinical trials (14
). For a 4-meter walk test, a usual gait speed less than 0.6 meters per second (m/sec) confers high risk for adverse outcomes, while a value greater than 1 m/sec confers low risk (16
). As shown in , the criterion for detecting a small meaningful change in gait speed using a 4-meter walk test is 0.05 m/sec, while the value for a substantial meaningful change is 0.10 m/sec. A related test, which has been used most commonly in studies of cardiovascular, pulmonary, and peripheral vascular disease, is the 6-minute walk, in which the distance walked over six minutes at one’s usual pace is measured (17
). The criterion for detecting a small meaningful change using the 6-minute walk test is 20 meters, while the value for a substantial meaningful change is 50 meters.
Other tests that have been used to assess lower extremity functional limitations include turning 360 degrees and climbing a flight of stairs, each of which is included in the Physical Performance Test (18
), one of the earliest composite measures of physical performance. To assess upper extremity functional limitations, several performance-based tests have been used (18
), including (among others) writing a sentence, picking up small objects, buttoning a shirt, pegboard, and functional reach. Although not a pure measure of functional limitations, grip strength, as assessed by a handheld dynamometer, is a robust predictor of disability and other clinically relevant outcomes (22
To reduce potential ceiling effects, especially among high functioning older persons, more challenging tests of physical performance have been developed for inclusion in longitudinal studies. For example, in the Health ABC Study, which included nondisabled persons aged 70–79 years, a long-distance corridor walk was developed, which assesses walking speed over 20 meters, distance covered in 2 minutes, and the time to walk 400 meters; and the SPPB was modified by extending the times for the three standard balance tests from 10 to 30 seconds and adding a single leg stand test (23
). Performance on the long-distance corridor walk was subsequently shown to be strongly associated with total mortality, cardiovascular disease, and mobility disability (24
Although functional limitations may also be assessed through self-report or proxy report, relatively few instruments focus exclusively on functional limitations. The best contemporary measure may be the function component of the Late-life Function and Disability Instrument (25
), which includes 32 items across three domains: basic lower extremity function (e.g. reach overhead while standing), advanced lower extremity function (e.g. walk several blocks), and upper extremity function (e.g. unscrew lid without assistive device). While this comprehensive measure has high reliability and validity, its responsiveness to clinically meaningful changes is uncertain.