Long-term use improves strength, delays the age at which ambulation is lost by 1.4 to 2.5 years, improves timed function testing (a measurement of how fast a child completes a functional task, such as walking or getting up from the floor), improves pulmonary function, reduces orthopedic complications (eg, the need for scoliosis surgery), stabilizes cardiac function (eg, delays onset of cardiomyopathy until 18 years of age), and increases survival by 5 to 15 years (1).