Your mid/low back gets loose every rep I saw in that last DL video. Part of that is a core strength issue, but I think part of it is form related. You're looking at the floor during most of every rep. You do a little better on the last rep of the last set. Try to look straight ahead or a little up at the end of your setup as the bar is leaving the floor and keep your head up through the pull. That might help keep your back from rounding as much, and it will help keep your weight back, which should help you pull everything a little faster. Watch some of my recent DL vids and see what I'm doing with my head position.
https://www.youtube.com/user/pkrizrgd/videos My coach has been on me about keeping my head up and I think its helping.
Last edited by cha59; 05-13-2015 at 01:19 AM.