Physical fitness is an important element of clinical exercise physiology. It is a multidimensional concept that has been defined as a set of attributes that people possess or achieve to perform physical activity. Many children with a chronic condition or disability have a hypoactive lifestyle. However, physical fitness and physical activity is just as, or even more, important in children with chronic conditions as in healthy children. Therefore, children with a chronic condition should not be "sidelined", but should actively participate in physical activity/sports.