Assessment of Functional Capacity in Clinical and Research Applications An Advisory From the Committee on Exercise, Rehabilitation, and Prevention, Council on Clinical Cardiology, American Heart Association

Afundamental requirement for many of the activities of daily living is the ability to perform predominantly aerobic, ie, oxygen-using, work. Such activities require the integrated efforts of the heart, lungs, and circulation to deliver oxygen to the metabolically active muscle mass. Thus, the assessment of functional or aerobic exercise time or peak oxygen consumption provides important diagnostic and prognostic information in a wide variety of clinical settings. Furthermore, numerous clinical trials, especially those in patients with heart failure, have used aerobic exercise time or peak oxygen consumption as a primary or secondary end point. This brief advisory will highlight the major clinical and research applications of functional capacity assessment. For a comprehensive review of exercise testing, the reader is referred to the American College of Cardiology/American Heart Association Guidelines for Exercise Testing.1 The maximal capacity of an individual to perform aerobic work is defined by the maximal oxygen consumption (Vo2max), the product of cardiac output (CO) and arteriovenous oxygen (AV O2) difference at exhaustion. Although Vo2max is measured in liters per minute, it is usually expressed per kilogram of body weight to facilitate intersubject comparisons. Functional capacity, particularly when estimated rather than measured directly, is often expressed in metabolic equivalents (METs); 1 MET represents resting energy expenditure and approximates 3.5 mL O2 · kg−1 · min−1. Because Vo2max is typically achieved by exercise that involves only about half of the total body musculature, it is generally believed that Vo2max is limited by maximal CO rather than peripheral factors.2 Vo2max is affected by age, sex, conditioning status, and the presence of diseases or medications that influence its components. Vo2max in a young world-class male …