Muscle Groups Addressed - Core, Shoulders
The knee tuck is one of my favorite ab exercises. In addition to micro-targeting your abdominals with the crunch motion, the jack knife works your obliques and core stabilizing muscles.
You'll need a stability ball for the gym version - or a chair with wheels for the work version. Begin in an elevated plank with your feet up on the stability ball, fairly close together. For an easier version, rest your shins on the ball. For a more advanced variation, stay up on your toes. Keeping your arms perpendicular to the ground, exhale slowly, contract your core, and roll the ball in with your feet. Keep your body as calm as possible (you might shake a little bit), as you bring your knees in as far as you can to your chest. If you can contract the entire way, your feet will be sitting flat against the ball at this point. Now inhale as you extend your body back to the starting plank position. Shoot for 10 repetitions.
If you don't have a rolling chair at work, get into an elevated plank on any sturdy, stationary surface and tuck your knees in to your chest, one leg at a time, leaving the other leg planted on the chair.
