The Back Extension is one of my favorites for developing bigger, stronger glutes and hamstrings.
Here’s how to increase glute and hamstring recruitment, and avoid cranking on your lower back. (45° Back Extension shown in video)
Instead of arching your back hard and targeting your lower back to perform the movement:
Keep a neutral spine.
Get a nice stretch in your hamstrings on the way down, and squeeze your glutes hard like you’re trying to crack a walnut between your butt cheeks to come up.
Finish with your glutes, driving your hips into the pad.
I generally like to do these towards the end of my squat or deadlift session for 3-5 sets of 8-20 reps, with 60-90 seconds rest.