Place your hand on the wall under the height of your shoulders. Keep your spine in 'neutral' and deep abdominals activated. Keeping your elbow straight, slowly let your body move towards the wall, and your shoulder back - slowly letting it 'retract' (moves towards the midline of your spine.) Then push your hand into the wall and your body away from the wall, making your shoulder blade wraps around the sides of your rib cage and your shoulder moves forward. Try and perform this movement by activating the muscles underneath your armpit. The other hand can rest behind your back with your thumb on the tip of your shoulder blade so that you can feel the movement. DON'T round your spine, keep it flat and make sure you keep your chest square to the wall at all times throughout the movement and do not tighten your neck muscles, keep trying to drop your shoulders away from your ears.

Progression: Try moving your feet further away from the wall to make it more difficult.