A modified deadlift. Feet at shoulder width, with hands grabbing the barbell just outside of your legs. Your hips will be higher than a normal deadlift to maximize posterior chain demand. Maintain a straight spine with shoulders pinched back. Pull the weight up. You can drop the bar from the top or lower it, but don’t “bounce” the weight for the next rep. See video for details.
This exercise can also be completed with a sandbag or dumbbells/kettlebells.