Plank Jacks: How To Do Them & Why Your Workout Needs Them 

A plank jack sounds like something you might find in aisle 33 at Home Depot, but it’s actually a potent exercise that’s becoming increasingly popular in HIIT, core, and circuit training classes. It’s time you found out how to do a plank jack, the muscles it works, and how you can fit it into your workouts for better core strength and greater conditioning.