Back Arch & Twerk Out :-p
How do you increase your back arch ?..and what are some good twerk - out videos online ? Lol
Cobra pose, sphinx pose, rocking bow, (or just plain non-rocking bow), supermans, cat cow, bird dogs, yoga bridge, and probably deadlifts and good mornings too since they strengthen that muscle you need to flex for a good arch. I think all of these you can search for by exercise name here in Skimble, our find easily online.