This exercise works the obliques muscles and the intercostal muscle groups at the sides of the waist. Plus it is a good exercise that also works your core and secondary muscle groups like your arms and legs. You can do this exercise with either 2 dumbbells or with 1 dumbbell at a time per side.
I will show you how to do this exercise using 1 dumbbell at a time per side, but my video below will demonstrate both ways of doing this exercise.
Now repeat the same procedure on your left side for your left obliques, performing the exact same number of repetitions.
My HD video below demonstrates the side bends obliques exercise using both 2 dumbbells or 1 dumbbell at a time.