As simple as it may be, I find it so difficult to understand which is the chest role in a push-up (and so I don't have the proper mind-muscle connection on how activate my chest).
Chest, as said here, performs the horizontal adduction, as shown in the following picture. When the chest is gradually shortened, point A (centre of bicep) moves toward the point B (centre of chest).
Well, what does this movement have to do with push-ups?
What I see in the push-up movement pattern seems to me just a forearm extension performed by the triceps. The distance between the centre of bicep and the centre of chest seems to me about the same in the starting and ending position. I don't see any significant shortening of this distance during the execution. So, by the common pictures that show push-ups, it seems to me it's a pure triceps, exercise. But it's known it's not... so which is the role of the chest?
To make a comparison, I may easily see the role of the chest in dumbbell bench press. In this case, as shown in the following picture, the distance between the centre of bicep and the centre of chest is shortened as the dumbbells are lifted, since they are brought close together.
But in a push-up the hands position is fixed... we can't do such a triangular movement that activates the chest.... Where is my mistake?