Although the burden of sickle cell anemia (SCA) on affected individuals is significant, few studies have examined the influence of having SCA on such measures of physical function as exercise capacity. Moreover, the physiologic basis of poor physical functioning in children with SCA is unknown and has not been studied extensively. The purpose of this proposal is to use cardiopulmonary exercise testing (CPET) to gain a comprehensive understanding of exercise capacity, as a measure of physical function, in children and young adults with SCA. The specific aims of this project are to: 1) Measure peak oxygen consumption (VO2), the reference standard for exercise capacity, in children and young adults with SCA classified by primary pathophysiologic contributor to their decreased exercise capacity, and 2) Examine the acute inflammatory response, measured by an increase in soluble vascular cell adhesion molecule (sVCAM) activity, in subjects undergoing CPET. These aims will be performed in 60 subjects with SCA and 30 matched controls without SCA. In a secondary analysis, we will also study the impact of baseline exercise capacity and the inflammatory response to exercise on short and long-term disease related morbidity. This study is essential because it will address several areas of exercise capacity, including the physiologic contributors to exercise limitation that remain fundamental knowledge gaps in SCA.