Place one hand on a bench in a push-up position while holding a dumbbell in the other hand. Reach dumbbell towards the ground then drive your elbow back using your back. Return to straight while keeping your core tight. You can do this exercise on your knees if you need a modification.
<iframe src="https://player.vimeo.com/video/271011272?background=1" width="640" height="360" frameborder="0" allowfullscreen></iframe>