Sore ribs?

So I'm a bit poo at posting here much and I don't put my pole up as much as I'd like either but I've been having a play today trying something that was suggested on the boards (can't remember who by sorry) about holding the pole around shoulder height and lift knees up to strengthen for inverting.. and now my ribs feel kind of achy, not hugely sore or anything to worry about I'm just wondering if it's normal or if I'm not engaging muscles enough and I need to fix it? B x