The involvement of this muscle affects the breathing in Duchenne muscular dystrophy

The correct option is Diaphragm.

Duchenne muscular dystrophy (DMD) is a progressive, genetic muscle-wasting disorder caused by the lack of a protein called dystrophin, which is essential for maintaining the structural integrity of muscle fibers. Over time, this leads to muscle damage, weakness, and degeneration throughout the body.

The diaphragm is the primary dome-shaped muscle located at the base of the chest cavity that drives respiration. During inhalation, the diaphragm contracts and moves downward, expanding the chest cavity to draw air into the lungs. During exhalation, it relaxes, allowing air to be pushed out.

As Duchenne muscular dystrophy progresses, it eventually affects the respiratory muscles, particularly the diaphragm. The weakening and scarring (fibrosis) of the diaphragm muscle significantly compromise its ability to contract effectively. This leads to a decline in pulmonary function, shallow breathing, difficulty clearing airways, and eventually respiratory insufficiency or failure, which is a leading cause of morbidity in DMD patients. The other muscles listed—the biceps, triceps, and quadriceps—are limb skeletal muscles involved in movement and mobility, but they do not play a direct role in the mechanics of breathing.