The serratus anterior muscle is too weak to exert its force stably (not surprisingly, your barbell must be shaking all the time), so it is normal to exert force unilaterally beyond control and slightly strain.

The lung is a string of balloons. Except the trachea and bronchi, the airflow is very small or even weak, which is similar to the air in the lower lung. Unless you deliberately take a deep breath, it is difficult to mobilize the bifurcation that is often said in sports. It is not excluded that the lungs are really uncomfortable, but most of the pain related to knee pads is caused by the traction of the anterior serratus diaphragm and intercostal tissue.

Then for this kind of situation, which is not even an injury, it is good to pull a hot sauna three or five times a day.