trouble getting deep breaths when doing fundamentals movements

I just wanted to check if this was normal. When I am doing the "hollow" for example in week 2 of the fundamentals (a hold at a half-way sit-up sort of position, on your back with shoulders and legs held up off the ground), the video recommends continuing to breath while holding, but I can barely get any breath in. 

Is this a sign of ab weakness or some other problem, or is this normal?

Thanks!

HI Peter, this is normal in case of a weak core. generally speaking the higher the intensity the harder it is to breathe.