Exercise Ball Prone I Extension
The guy in the picture looks like he is either having a lot of fun with a big smile or he is grimacing because this is a tough exercise. Try it out and see if you can figure out whether he is enjoying those shoulders burning like you will feel!
Lie face down over an exercise ball with your arms to the side straight back while making a fist. Slowly bring your upper back inward and hold for 2 seconds before returning to original position. Try not to shrug your shoulders.