Q. A 16 year-old girl presents to the muscular dystrophy clinic with progressive weakness over the past several months. She is having trouble climbing stairs, getting up out of chairs, and raising her arms above her head. On exam, she has profound proximal upper and lower extremity weakness and wasting that is symmetric. Her CPK is greater than 30,000. She has been told she has a muscular dystrophy and has been very curious about muscle cells. Her uncle works in a genetic engineering laboratory and she would like to find a cure for her illness. She asks you about myofibrils. In regards to myofibrils, the thin and thick filaments do NOT overlap in which of the following areas?