The New Rules of Abs
Master these seven static floor exercises.
The basic plank—toes and forearms on the floor, shoulder blades pulled and down, butt down, body straight—is harder than you might realize. But once you can hold it for 60 to 90 seconds with ease, move on to a more challenging version of the classic. (The exercises are organized in ascending order of difficulty.) Do them in front of a mirror so that you can monitor your form, and be sure to break when it goes off.
Side Plank with Feet Elevated
Make sure your butt doesn't drop, that your shoulder blades are pulled back and down, and that you aren't tilting—your upper shoulder should be pointing straight at the ceiling.