Similar to exercises like Stiff Leg Deadlifts, Back Extensions which place isolated shear forces across the lower back. Good Mornings place even higher stress across the lower back due to the weight being placed on the shoulders increasing movement of inertia and shear forces through the lumber spine.

Moral of the story is don’t be a hero and go to heavy – ( Good Alternatives Deadlifts, Bulgarians Splits, 1/2 Deadlift)