This review summarizes the research relating physical activity to aerobic fitness among adolescents. A brief description of commonly used physical activity and aerobic fitness measures is presented, followed by an interpretation of the literature that suggests a small to moderate relationship between physical activity and aerobic fitness in this population (typical correlation of .16-17). Dose-response data are lacking, which makes it difficult to offer definitive conclusions concerning the amount of physical activity necessary to elicit change in aerobic capacity. Nevertheless, recommendations about the type, amount, and quality of physical activity for adolescents are presented. Recommendations are based on a summary of the research data on daily physical activity and aerobic fitness in adolescents. Further research is needed to investigate the association between habitual physical activity and aerobic fitness in adolescents where the a priori goal is to identify a threshold of daily physical activity n...