T he current era is characterized by kinetic limitation, both in children, and adolescents. Children today expend 400% less energy than did their counterparts of 40 years ago and are 40% less active than they were 30 years ago. Children and adolescents' today activity level is very low, while they spend their free time, mainly, in sedentary behaviours, such as tv viewing, and computer videogames playing. The average child or adolescent 2-to 18-years old spends on tv-videotapes watching or video games playing more than 5 hours per day. The lack of movement in children and adolescents' lives is one of the primary predisposing factors of increased morbidity, since many of the chronic diseases of adults are initiated in childhood. Approximately 40% of children aged 5 -8 years old present increased risk factors for heart disease, such as obesity, hypertension and high total cholesterol, or for diabetes. These diseases are most often irreversible due to the continuous sedentary lifestyle that has been adopted by children. Moreover, significant relationships between inactivity and other adverse health practices, such as consumption of less-healthy foods or increased fat intake, as well as cigarette smoking that have been demonstrated in adolescents, predispose to cardiovascular disease. To sum up, inactivity represents a behaviour that is associated with adverse health consequences which initiate even though from childhood and follow children and adolescents throughout their lives.