Core strength and Brazilian jiu-jitsu really go hand in hand. It’s hard to have one without the other, but building your core in the ways that truly support your training can be difficult. Trunk rotation is one of the most underrated aspects of core strength. Washboard abs are great and all, but if you lack the fundamental rotation skills, they won’t benefit your game much.
Grab a stability ball and get to work! (It’s also a good idea to try these on a surface that won’t break your face if you spaz out.)