The patented Stealth® Core Trainer turns the boring plank exercise into a fun, gamified workout that trains your core, arms, and chest all at the same time. It carefully calibrates with your phone's motion detector to recognize your movements. It then translates those movements into game play actions on the screen of your phone. Simply download the FREE App with Gamified Workouts onto your smartphone. Games never play out the same way, so you'll always be in store for something new and exciting. holds up to 3 units, providing convenient and attractive storage.