source: Pediatric Orthopaedic Society of North America (POSNA)
Weakness is noted from early childhood with delay in walking, and difficulties with balance. Almost all children will achieve ambulation (average age 2 years). Many children will present as new onset toe walkers as they compensate for quadriceps weakness. Weakness progresses throughout the first decade of life. Gluteus maximus weakens first resulting in a lordotic gait. Most children lose the ability to ambulate early in the 2nd decade of life. Upper extremity function will decline as well with loss of shoulder elevation and hand to mouth activity occurring in many by the middle of the second decade. Pulmonary function exhibits a slow and steady decline. Cardiomyopathy is often evident.