Functional capacity testing typically involves musculoskeletal evaluations using instruments such as inclinometers, goniometers, range-of-motion machines, and strength analyzers. Depending on the organ system to be tested, a variety of tests are available to assess physiological competency (eg, liver function or renal function tests). The cardiopulmonary exercise test (CP Ex test) is one test that defines work capacity and addresses the two primary issues necessary for muscle movement: the adequacy of the cardiac output and that of the lungs to acquire oxygen and excrete carbon dioxide. A normal test requires correct functioning in five organ systems: the heart, the lungs, the hematopoietic system, the vascular system, and the muscles. The CP Ex test can discriminate between individuals with poor exercise capacity caused by hyperventilation, obesity, or malingering. The CP Ex test is not required when one is rating impairments according the AMA Guides to the Evaluation of Permanent Impairment, but the test may help physicians understand the basis for decreased exercise tolerance, thereby facilitating the impairment rating process. Finally, the CP Ex text is useful for assessing functional capacity but does not address all the physiologic, anatomic, and functional issues—no single test can do so—but the CP Ex test provides a very adequate way to address an individual's functional capacity.