Pain after deep breathing after a chest bump is common for the following reasons: 1. Local soft tissue contusion: the most common. As the thorax has to stretch and contract during deep breathing, the process of stretching and contraction pulls the soft tissue of local contusions, which can cause pain. 2, post-impact fracture: If the violence of the impact is very large, it may lead to fractures in the chest, such as sternal fractures or rib fractures. 3, pneumothorax or Hemopneumothorax: Some patients may also have pneumothorax or hemopneumothorax along with lung contusion, and a clear diagnosis can be obtained through chest X-ray or chest CT examination.