Begin on all fours with your hands directly below your shoulders and your knees beneath your hips. Keeping your core engaged and your back flat, lift your knees so they're hovering over the mat.
Bring your right hand back to tap your left knee, lifting your foot off the ground to allow the two to meet. Return your hand and foot to the mat, then alternate, tapping your left hand to your right knee.
Continue alternating hands and knees for 40 seconds.