Tighten your core with this slimming ab exercise.
Planks are popular on-the-ground ab moves for a reason (they work!). Adding the stability ball forces you to keep your body balanced and flexed, adding a level of difficulty to the traditional plank.
To make it even harder, do 5 pushups in between each plank, which will work your arms, shoulders, back, and core.
How to do it: Place your shins and tops of your feet on a stability ball with your hands on the ground in plank position (shown). Engage your core, squeeze your butt muscles, and hold for 1 minute.
Try this exercise: On-the-Ball Plank