Pull: Bring the bar back up the reverse way you lowered it: mostly through trunk extension with a slight extension of the knees. (muscle-fitness-training.com)
Comparing the prone trunk extension with standard compound exercises, Hamlyn et al. (2007) compared the back squat and conventional deadlift with 80 % of 1RM to the superman exercise performed on a swiss ball. (strengthandconditioningresearch.com)
Using a little more trunk extension is okay as long as you are not compromising your postural position (i.e. don't go into lumbar hyperextension or hyperflexion). (kingofthegym.com)