Begin in the plank position, with your shoulders over your wrists, your body in one straight line, and your feet together.
Like the motion of jumping jacks, jump your legs wide apart and then back together to complete a rep. Jump as quickly as you want, but keep your pelvis steady and don't let your booty rise toward the ceiling.
Complete as many plank jacks as you can in 40 seconds. Take a 20-second rest.