There is hardly a core exercise more basic or notorious than the plank. And when performed “actively”—meaning you’re engaging every muscle you can, from head to toe—it neutralizes the spine and taxes your entire body, which, according to Chris Frankel, head of performance at TRX, “brings awareness to alignment and posture with intention and strength.”

Unfortunately, most people “passively plank,” which visually resembles a proper plank, but doesn’t feel like one, and does nothing to bolster core strength.

So, check for any of the following blunders to make sure you’re getting all the benefits.