Final answer:
Chest muscles grow large in emphysema due to the increased effort required to breathe caused by the breakdown of lung tissue.
Step-by-step explanation:
Chest muscles grow large in emphysema as a result of the increased effort required to breathe due to the breakdown of lung tissue. In emphysema, the lungs lose their elasticity, making it difficult for air to flow in and out. To compensate, the chest muscles, including the intercostal muscles, work harder to expand the thoracic cavity and facilitate breathing, leading to hypertrophy or enlargement of the chest muscles.