Mine was already pretty tight from squats and I only did one set of these well only 8 reps before I gave up , I didn't notice any difference really. Maybe had I done more it may have tightened up more.
I saw a guy that had middle back surgery doing squats once standing on two boxes. He placed two 24" boxes about a foot apart , had a weighted dip belt around his waist and he would squat over the crack in the boxes letting the weight lower between them. That might have the same effect as "somersault" squats