Start by lying flat on your back. Gently press your spine into the ground and lift your legs off the ground, bending them so you form a 90-degree angle with your shins parallel to the ground and your thighs perpendicular. Place your hands behind your head with your elbows wide and brace your core to lift your head, neck, and shoulders off the ground.
Bring your right knee in toward your chest as you extend your left leg straight out, simultaneously bringing your left elbow across your body to meet your right knee.
Repeat on the other side, bringing your left knee toward your chest and reaching across with your right elbow.
This counts as one rep. Continue alternating your legs back and forth, doing as many reps as you can with proper form in one minute.