Endurance
Endurance is the ability to maintain a given level of exercise over time or
to perform a given task repeatedly without fatigue that prevents further such
activity. This factor is rooted in numerous physiologic parameters: air exchange
in the lungs, heart function, blood circulation and patency of blood vessels, and
the biochemical characteristics of individual muscle cells. Diseases or conditions
such as coronary or peripheral vascular disease, restrictive or obstructive pulmonary
disease, general deconditioning, and malnutrition may therefore adversely
affect endurance.
Several terms are used to monitor endurance. VO2 peak represents the peak
amount of oxygen that may be transported to the active muscles during exercise
and is used extensively to chart progress in cardiac and pulmonary rehabilitation.
Exercise intensity and caloric expenditure in general may be defined in
terms of metabolic equivalents, or METs, where one MET is equivalent to the
oxygen uptake of a person at rest or approximately 3.5 mL per minute. Subsequent
METs represent multiples of this basal rate. Housework, such as vacuuming
or mopping, uses approximately two to four METs; moderate exercise
such as jogging uses five to six METs. Exercise over six METs is considered
high intensity.
Elderly patients develop poor endurance as a result of many factors. Aging
itself is associated with declining skeletal muscle mass and capillary blood flow,
poor nutritional intake, and impaired oxygen uptake [43]. In addition to these
factors, several common disease processes in elderly patients are shown to affect
endurance. Approximately 11% of patients older than 70 have chronic obstructive
pulmonary disease, which further decreases oxygen exchange in the lungs [44].
In addition to being a common cause of poor endurance, cardiovascular disease
(including CHF and CAD) is the second most common ailment and the leading
cause of death in older people [45]. General deconditioning from inactivity is
common in older adults and contributes to poor endurance [46]; it may predispose
to diabetes mellitus. With its associated neuropathies, pain syndromes,
and attendant risk for cardiac disease, diabetes is both a risk factor for further
inactivity and poor endurance and the sixth leading cause of death in adults
65 and older [47].