Move forward with springy strides, swinging each leg out in front of you straight-kneed, reaching your hands toward the rising leg as it comes up. Push off the ball of the back foot to add a light bound to every stride and keep your torso tall. Somewhere between a toy soldier and a sprinter's drill - the knee stays proudly straight, and the spring comes from the ankles, not the knees.

Works: hip flexors, hamstrings, quads, calves

Breathing: Steady and rhythmic, in time with the strides.

Common Mistakes: Bending the knee as the leg swings up, hunching forward to meet the leg instead of staying tall, and shuffling flat-footed with no spring in the stride.

Make Easier: Slow it to a walking pace with no bound, go out-and-back or march them on the spot if space is short, or build up with Butt Kicks first.

Make Harder: Swing the legs higher and add more spring to each bound, or alternate rounds with High Knees to keep the heart rate climbing.