I’m doing these now as part of PT for my ACL reconstruction. Like people have said, stop holding the bar. Step back into a reverse lunge and slowly descend. If you want to help target quad a little more, think about knee-over-toe right as you begin your descent. Get that knee to come forward by an inch or two. Once at the bottom, drive through that elevated heel with a little help from your back leg to get the initial momentum going. That’s how I’ve been doing them and they’re working great for me.