Why does Holden have difficulty breathing after a short run to the main gate?

Holden Caulfield experiences difficulty breathing after a short run to the main gate due to his underlying emotional distress and anxiety, which manifest physically. His mental state, characterized by feelings of alienation and depression, can lead to heightened physiological responses, making exertion feel more exhausting. Additionally, his general lack of physical fitness contributes to this shortness of breath, reflecting his overall struggles with both mental and physical health.