Core

First of all, your "core" is your abdominals (transverse, rectus and obliques OR deep, front, sides), your bum and your back.

Think of this: from your belly button, your strength of movement extends out like a spiderweb. Once you've engaged and braced your core muscles, EVERY other movement is an extension of that and becomes easier.

Pull your abdominal muscles IN and UP towards your belly button as if you are trying to squeeze into your skinny jeans! There - feel it?
There are numerous "core training" classes out there now. Be wary - if these are not instructed by someone qualified, you might be doing more damage than good.

I advise you to SEEK a personal trainer who can teach you how to SAFELY and EFFECTIVELY strengthen your abdominal, glutes and back muscles (like....ME!) and THEN get along to...

mountain climber

pilates
CX WORX
yoga
Ab Blast