The Keystone Deadlift is a great way to build the hamstrings, glutes, and lower back. In other words the posterial chain.
Notice this lift may begin from the "finished" position by lifting the weight off of a rack. You should strive to push the butt and the belly out, somewhat mimicing the position of one of the old keystone cops, whence the name. This position allows for a nice "pre stretch" on the hamstrings.
From there it is lowered much like a Stiff Legged Deadlift while maintaining
the butt/belly out position, but it stops short of touching the floor.
The bar should stop right at or just below the knees.
Notice the back is flat and our model is actually bringing the
bar back toward her as she pulls.
This movement should be performed slowly under control.
The knees should have a slight bend in them at all times.
If performed correctly you will feel it in the hamstrings and glutes.
If you feel it in the lower back rethink your positioning.