The Press Stud Visualisation
The next time you swim, think about how your shoulder blade might be lifting away from your back as your shoulder rolls forwards. Imagine you have Press-Stud (also known as a clothes popper or snap fastener) attached on one side to your shoulder blade and on the other side to your back:
Paul explains more:
A higher arm recovery means less chance of the hand catching on the surface and makes it less likely to cross the centre line in front of your head as you enter into the water. Your roll should also be improved as the improved posture helps drives your rotation through the water along the long axis of your spine.