More young females train for competitive sport today than ever before. Yet the understanding of girls' capabilities for endurance training is limited. Many studies on the development of endurance capabilities are cross-sectional and are unable to control for the changes that occur as a result of normal growth, development, and maturation. Because body size significantly affects the measurement of physiological performance, endurance measures such as peak oxygen consumption (Vo2) should be normalized or scaled to account for the differences in body size. Inappropriate analyses of peak Vo2development have clouded the understanding of the independent contributions of body composition to the growth of peak Vo2in females. Of the research available, it is suggested that girls' endurance capability increases as they increase in size until puberty, then plateaus as they progress to adulthood. However, much variation exists based on genotype and on the frequency, intensity, time, and type of endurance training program. Further longitudinal research is necessary to clearly address the endurance exercise capabilities of young, growing females.