Stand up straight facing a wall.
Place your hands on the wall around both shoulder height and width.
Step back so that your arms are straight.
Keeping a straight line from your heels up to the top of your head, bend your elbows, bringing your chest in towards the wall.
Keep your gaze directly ahead.
Allow your elbows to bend into the side of your body.
Push through your hands to straighten your arms back out again and repeat.