Instead of lying on a bench, lie on a Swiss ball and place your hands flat on the floor.
Set a pair of dumbbells on the floor in front of you.
Bend at your hips and knees, and grab the dumbbells with an overhand grip.
Without allowing your lower back to round, stand up with the dumbbells.
Lower the dumbbells to the floor. (If you can’t lower the dumbbells all the way to the floor while keeping a slight arch in your lower back, stop just above the point where it starts to round.)