I did most of my shoulder exercises sitting down which makes the exercises more difficult to do vs standing. Moves like side/front raises and shoulder presses- when you do them standing, your legs are helping you lift the weight. Try doing all your sets sitting on a chair or bench. You will find that you can't lift as heavy as you do when you are sitting vs standing. It's good to mix things up and keep our muscles guessing. I did the same cardio as Monday.