Thanks for the recs. I've seen these in books under their German names but haven't tried them yet. (In German the plank on your forearms is called Unterarmstütz, the side plank Seitstütz.) Looks like I will get some more use out of my stopwatch in the future.

I have been having some success already with my core muscles in that at least I can feel them now properly and tense them while breathing more or less normally. Initially I had a really hard time to tense them without accidentallynholding my breath entirely.