Start in a push-up position with your feet together and your body in a straight line. Keeping your hands planted and your torso still, jump both feet out wide, then jump them back together - the leg pattern of a jumping jack performed in a plank. Land on the balls of your feet, softly enough that your hips don't bounce, and hold your shoulders steady over your hands from the first jack to the last.

Works: abs, shoulders, glutes, hip abductors

Breathing: Exhale as the feet jump out, inhale as they come back - or settle into one breath every two jacks at speed.

Common Mistakes: Letting the hips pike up or bounce with every jump, rocking the shoulders back behind the hands, and landing hard with locked knees.

Make Easier: Step the feet out and in one at a time instead of jumping - same pattern, no impact - or shorten the sets and rest in the plank.

Make Harder: Drive the pace up with the hips pinned level, or move on to Plank Jump-Ins or Plank Step-Outs.