What is the effect on muscle fibers when dystrophin is deficient?

• A. They become more elastic
• B. They break down with use
• C. They resist fatigue
• D. They increase in strength

Answer: (B)

Dystrophin normally anchors the muscle fiber’s internal skeleton to the surrounding matrix, keeping the membrane stable during contractions. When dystrophin is missing, the sarcolemma becomes fragile and tears easily with use. Those tears let calcium and other damaging ions flood into the fiber, triggering proteolysis and inflammation that cause the muscle fiber to die. Over time, repeated damage and insufficient repair lead to loss of muscle fibers and replacement with fibrous and fatty tissue, producing progressive weakness. So the primary effect is that muscle fibers break down with use. The other options don’t fit because the fibers do not become more elastic, they do not resist fatigue better, and they do not gain strength; they actually weaken and degenerate with activity.