Cardiopulmonary exercise stress testing (CPET) provides objective data to assess cardiac and pulmonary impairment. This article discusses changes in the CPET section of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides). The explanation of CPET in the AMA Guides, Sixth Edition, adds a single word, “static,” that significantly effects how this test should be conducted. Routine pulmonary function tests (PFTs) provide information about a person's ability to breathe, eg chronic obstructive pulmonary disease or asthma can stratify the severity of these diseases; they do not measure the ability of the lungs or heart to provide adequate oxygenation to metabolizing tissues. Static tests of lung function are the norm when diagnosing asbestosis, and the typical abnormalities seen are restriction, some airflow obstruction, and a diminished diffusing capacity. These abnormalities correlate linearly with the degree of abnormality found radiographically. In individuals with unexplained shortness of breath with exertion or fatigue that is not easily explained in the medical records, a CPET will allow secure diagnosis of causation. Thus CPET is a powerful tool to explain shortness of breath with exertion or fatigue, and CPET has a role in the impairment rating process of all individuals with interstitial lung diseases and in selected individuals with unexplained symptoms.