Stand with your feet together and your arms relaxed by your sides. Jump your feet out wide, then jump them back together, in a continuous rhythm - it's the leg half of a jumping jack, with your arms staying low and loose instead of swinging overhead. Land softly on the balls of your feet with your knees bending to absorb each landing, and keep your torso tall throughout.

Works: quads, glutes, calves, hip abductors

Breathing: Steady and rhythmic, in time with the jumps - settle into a pace you can hold.

Common Mistakes: Landing hard on flat feet with straight knees, leaning forward from the waist, and letting the jumps get narrower as fatigue sets in.

Make Easier: Take the impact out - step one foot out to the side and back in, alternating sides at the same rhythm.

Make Harder: Speed up and jump wider, or add the arms back in with full Jumping Jacks or Seal Jacks.