Plank Jacks

Begin in plank position, with your shoulders over your wrists, your body in one straight line, and your feet together.
Like the motion of a jumping jack, jump your legs wide and then back together. Jump as quickly as you want, but keep your pelvis steady and don't let your booty rise toward the ceiling.
Do a total of 30 jumping jacks, which counts as one set. Then complete two more sets.