Whenever i do back lever's as part of my workout (I'm not a Gymnast just a calisthenics bodybuilder) my chest and ribs hurt, not very painfully but enough to cause bother. it's a sort of tight feeling and it goes away a few minutes after i stop the back lever. This pain doesnt seem to be a problem for my other exercises and i stretch my chest well before i begin, was wondering if anyone could shed somelight on what this could be since i think it's a mobility problem. thanks