Lie on your back, and lift your hips into a bridge position, firing up your hamstrings and your glutes.
Lift your toes, and begin to walk your heels away from your hips in small steps, keeping your hips as stable as possible.
Once you've walked your heels out as far as you can, lower your hips to the floor. Perform a crunch, lifting your torso as you draw your knees into your chest, and deeply engage your abdominal muscles. Hold the crunch for three seconds.
Lower your head and feet, coming back to a bridge position, to complete the rep.
Complete as many reps as you can for 30 to 60 seconds, followed by a 15- to 45-second rest.