I have no pro experience in training, I only do it myself at home. This is not actual shoulder-strike (a la Conor vs Cowboy) training. Its supposed to train your technique and develop the core. I am convinced this training method helps a ton getting the core and feet involved in your punches... helping build that muscle memory and adding a bunch of flexibility to your shoulders which in turn gives your punches a bit of reach. This also lets you target which areas you can improve as there are less moving parts for you to analyze. Anyway, the idea is to picture your opponent about 3 feet away, and pretend you can only strike with your shoulders, doing exaggerated torques. Footwork is key and straights are a bit trickier than hooks. For jabs, literally shoulder drop as you step/ stomp forward.