From a tall plank position, lift your hips up to the ceiling, while extending your right leg as high up as possible behind you, coming into a three-legged dog position.
Lower your right leg down as you reestablish the tall plank position and drive your right knee in toward your arms. Step your right foot behind you, coming back to the tall plank position.
Repeat with your left leg.
Continue alternating sides, completing as many reps as you can for 30 to 60 seconds, followed by a 15- to 45-second rest.