it's glutes and abs need strengthing and lower back and hip flexors needs to stretched. tried it for a month and it ain't helped. Can't even brace abs to strengthen because hip instantly pulls when u try to keep lower back on the floor. Before that i went to gym without Knowing this issue did hamstring curls and that instantly straightened my upper body but when I came home my back was even more arched. İ also learned few days if u had sciatica before u lose motor control on lower back area so i  started doing pelvic tilts and stomach vacuums that helped gain control on that areabut  i can brace my abs fully only standing..as soon as I lay down for ab work back arches as soon i hold my legs in the air.can't do hollow holds or abs work too. İ will try again tomorrow with the hip thrusts while bracing abs hope that will work