First up...hyperextentions are done mainly to focus on your hamstrings. Try to tighten them while doing them, also, don't go so high up, I see gusy flinging all up in the air, just go parralell. Try going slow too, none of this swining and flinging like a monkey, respect the equipment (not sayign you don't) I started light deads with proper form and back feels much better, i slipped a disc three years ago. Keep them light and slow. Tighten the glutes and hamstrings, try not to feel yoru back. Strethching is also key component.