Referring to the image below, the arm involved in the exercise is bent to 90 degrees throughout the exercise, as if doing hammer curls, only that the arm stays in that position throughout this exercise. The arm rotates on the shoulder to move the dumbbell towards chest and then away from it multiple times. There is not vertical movement; all movement is horizontal.
It seems to me the muscles moving the dumbbell towards the chest are a combination of shoulder and chest, and for moving away are the antagonist shoulder muscles and back muscles. From this it therefore seems that the amount of dumbbell weight mostly affects the bicep holding it up, not so much the muscles involved in rotating the dumbbell.
So, what is this exercise called, its purpose, and is the weight (when using a dumbbell) much of an influence on anything else besides the bicep?
This exercise makes sense if using horizontal resistance, for example when using cable as shown below, therefore putting the resistance on the shoulder, chest or back, depending on the side you are pulling from. But with a dumbbell, it seems completely redundant...