The explanation for Creatine kinase

Question 3 (1 point) What is the explanation for creatine kinase (CK) levels in a 14-year-old boy with Duchenne muscular dystrophy being much lower now than they were 5 years ago? Most of the muscle tissue has already been destroyed. His disease is improving. He now performs passive rather than active exercise. The disease is probably Becker muscular dystrophy (BMD) rather than Duchenne muscular dystrophy