SLDL's
but with a twist.
Stand with your legs stiff, straight as possible, bend over and extend and flex the spine, holding in the flexed (or contracted) position for 2 seconds, slowly lower for 4 and extend for 2
12 rep's max, as with all exercises, add 2.5kg to the bar when you can easily do 12.
Start off with 10kg each side of the bar to test, if you can do 12 easily, then add 2.5kg.
Do this once a week
You might want to do 3 sets of 10 without the bar to become competent at the movement
Be careful, move slowly, close your eyes and picture the erectors doing the work only.
Don't overly extend the spine, it's only going to be a small ROM