Children and adolescents possess higher weight-related maximum oxygen consumption (VO2max) levels than older individuals. The capacity of prepubescent children to improve aerobic fitness with endurance training is controversial, and reported data have provided conflicting evidence. In the adult, physical activity of certain form (endurance), duration (15-60 min), frequency (3-5 times per wk), and intensity (heart rate 60-90 percent of maximum) are necessary to improve VO2max with training. When training programs in children are examined, those regimens failing to demonstrate a beneficial effect on aerobic fitness are observed not to comply with adult standards. Conversely, despite important experimental weaknesses, exercise training programs in children which employ adult criteria often show improved VO2max similar to that observed in older subjects. At the present stage of knowledge exercise training programs directed toward improving aerobic power in children should incorporate exercise intensity and duration in accord with adult-related criteria.