The action mode of any action is mainly considered from two angles: training the target and avoiding injury. Generally, we do bench presses to exercise our chest muscles. If you do bench press, you can do it in the pectoral rib of pectoralis major, that is, in the middle of pectoralis major. The direction of muscle fibers in this part is parallel. The ideal action mode of bench press should be to make the pectoralis major exert better force, and then the barbell is placed above the pectoralis major, and the movement track of the barbell is always along the vertical plane of the pectoralis major, straight up and down. But in fact, in the initial position of bench press, the arm is perpendicular to the trunk, which is just above the shoulder joint, so the actual bench press trajectory is a diagonal line. The most common mistake many beginners make when doing bench press is that barbells can't follow this diagonal line. Why not? The angle between the upper arm and trunk is too large when bench pressing, because the shoulder joint is not stable enough and the scapula is not tightly contracted. This will lead to two problems. First, deltoid adduction compensation, more participation in the process of bench press, the training of the target muscle pectoralis major will be much worse; It is easy to increase the pressure and impact on the shoulder joint and cause injury. Finally, after reading the subject's head, it is estimated that there is not much shoulder exercise at ordinary times, and it needs to be strengthened, especially the training of scapular stabilizing muscles. Stability training should precede strength training, so don't rush it. I wrote an article about the mode of push-ups before. I suggest looking for it, just like bench press.