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

Holden Caulfield experiences difficulty breathing after a short run to the main gate due to his physical and emotional state. He is not in good physical shape, having spent much time in a more sedentary lifestyle, which contributes to his shortness of breath. Additionally, his anxiety and mental distress exacerbate his physical reactions, reflecting his overall sense of alienation and struggle throughout the story. This moment symbolizes his vulnerability and the weight of his internal conflicts.