"Grab your ankles, open your legs, and smile" might not be the kind of direction you'd expect from your group fitness instructor, but anyone who's tried Pilates has seen this move in action—and knows what a great workout it is.
Why you should do it: The open-leg rocker is not only great for strengthening your core, it also challenges your balance, flexibility, and coordination—three important aspects of fitness we often neglect.
How to do it: Sit with a straight back, tight core, and knees bent in front of chest. Lift feet so you're balancing on your sit bones. If this feels challenging, you can do the roll from here. To make it harder (and get the full embarrassing effect), extend both legs straight out in a "V," grabbing each ankle or calf. Once you're stable, roll onto your back, engaging your core the entire time, and then roll back up to balance on your rear without letting go of your legs.