It is normal. It is the ability of the human body to cooperate with breathing. In fact, it's not that your ribs become bigger and smaller, but that the muscles between the ribs are elastic, which expands outward when inhaling, making your chest bigger and helping you inhale ~ ~ This phenomenon will become obvious after you exercise, so you realize that it is the same at ordinary times, but the amplitude is not as big as after exercise.

Run 1000 meters, full marks. Very impressive ~ ~ _