Muscle weakness can begin as early as age 3, first affecting the muscles of the hips, pelvic area, thighs and shoulders, and later the skeletal (voluntary) muscles in the arms, legs and trunk. The calves often are enlarged. By the early teens, the heart and respiratory muscles also are affected. For more about DMD symptoms, see Signs and Symptoms.
Becker muscular dystrophy (BMD) is a milder version of DMD. Its onset is usually in the teens or early adulthood, and the course is slower and less predictable than that of DMD.