Admit it - you tried to this in the playground at school once. In the video for 'Smooth Criminal,' Michael Jackson was able to plant his feet and lean forward at an impossible angle without falling over. Magicians are often capable of achieving this illusion too.
Jackson and the magicians use the same method to do this - shoes with holes cut into them. The holes allow them to secure themselves to strong nails hammered into the floor, and then they can lean forward as far as they wish.