Measures of functional capacity have been widely reported
in the scientific literature, and many established measures
of this dimension are available. For example, the maximal
oxygen uptake is a measure of aerobic capacity and is assessed
during a symptom-limited exercise test. The 6-minute
walk test and the shuttle walk test are used to measure functional
capacity for walking. Similarly, tests of skeletal muscle
strength indicate functional capacity for strength. The
measurement of functional performance is less advanced.
One commonly used measure of functional performance is
the Functional Performance Inventory (FPI). Leidy (1999)
developed the FPI with people who had COPD; it has the
potential to be appropriate for other groups of people with
chronic illness, such as chronic congestive heart failure. In
addition, two scales from the SF-36 Health Survey (Ware
& Sherbourne, 1992) have been used widely to measure
functioning: the physical functioning and social functioning
scales. The SF-36 is a generic measure that can be used
with both healthy people and people with chronic illness.
Many investigators also have used the Sickness Impact Profile
to measure functional performance, but it is an indirect
measure of functional performance and a direct measure of
functional impairment.