The principle of respiratory movement has always been a difficult point in junior high school biology textbooks. Students always have more or less doubts when learning the changes of sternum and ribs during breathing exercises. Many teachers are used to letting students have such an experience: one hand is placed on the sternum, the other hand is placed on the ribs, and deep breathing exercises are done under the guidance of the teacher. When inhaling, the sternal ribs move upward and outward; When exhaling, the sternal ribs move downward and inward. Then I asked the students if they could feel it, and found that most of them had puzzled expressions on their faces. The quadrilateral scaffold model is still used in the teaching materials to explain, but it is found in the actual teaching that the problem is more abstract with this model. After repeated exploration, the author finally found that it is easier to understand the changes of sternum and ribs when breathing based on personal experience. The specific method is as follows: the teacher prepares 1 tape measure. During the experiment, the students took off their coats and touched a protrusion under the sternum, that is, the xiphoid process of the sternum. Sit on the chair with your legs slightly apart, press the first end of the tape measure on the xiphoid process of the sternum, tighten the tape measure and press it vertically down on the chair surface, take a deep breath and record the length of inhalation and exhalation. If the duration of inhalation is longer than that of exhalation, it is found that the sternum moves upward when inhaling, and vice versa when exhaling. Similarly, press the first end of the tape measure on a rib under the armpit, tighten it and press it vertically down on the chair to record the length of inhalation and exhalation. The length of inhalation is greater than the length of exhalation, so it is explored that the ribs move upward when inhaling, but the opposite is true when exhaling.