3) Deadlifts.

One of the most basic exercises done by bodybuilders. It works a wide array of muscles, in this case we’ll focus on the effect it has on the lower back.
The subject grasps onto a barbell which is in front of him/her, with about shoulder-wide grip, one hand overhand the other underhand. (this is to prevent the bar from rolling)
He/she then stands up pushing with the legs, back kept straight. When in a standing position he/she pulls the arms back and drives the chest out. Lowering the weight in similar fashion until it touches the ground, he/she is ready for another rep.
Extra considerations: Because of the big amount of weight that is used for this exercise, be extra careful in suiting it to your abilities. The risk of injury is always there.