Depending on your historical perspective, we are about to mark the 65th or 50th anniversary of the birth of pediatric exercise science. Robinson's remarkably prescient study at the Harvard Fatigue Laboratory in 1938 was really the seminal work that first defined maturational differences in physiologic responses to exercise ( 16). Then there is a bit of a gap in time until 1952, when P.O. Astrand published his landmark treatise on physical work capacity in children (2). Since then the field of pediatric exercise physiology as an investigational discipline has flourished. So now, with these anniversaries upon us, it's a good time to reflect on where we've been and where we're going. Now, I'm certain this didn't actually happen, but if a long-range planning committee had been convened in 1960 to establish goals and future directions for research in pediatric exercise physiology, the outcome would probably have gone something like this: "First, let's examine the physiologic responses to exercise as children grow, and let's find out if young people are (or are not) uniquely different in these responses compared to what we know about adults. Then, let's use this information to create therapeutic interventions for children with chronic disease, form guidelines for training young athletes, and provide strategies for preventive health in the pediatric years."Now 40 years have passed. If that same committee were to reconvene now, how would they grade our progress? For the first goal, we would surely get an "A." In the past 50 (or 65) years researchers have amassed a large volume of data indicating that children are in many ways unique in their physiologic responses to exercise. The most recent compendium to summarize the state-of-the-art in pediatric exercise physiology, Armstrong and van Mechelen's Paediatric Exercise Science and Medicine, is dramatically convincing of how much has been achieved in half a century (1). There is no question that as exercise machines, children are indeed different. Biological maturation clearly influences biomechanics, exercise economy, aerobic and anaerobic fitness, physical training, temperature regulation, body composition assessment, and physical activity patterns.To be sure, there is much more to be learned. Particularly our next steps in the area of basic pediatric exercise physiology need to be in the direction of understanding mechanisms. Why does anaerobic fitness relative to body size increase as . .