Begin lying on your back on a yoga mat. Extend both of your legs and engage your abdominal muscles by drawing your belly button in toward your spine. This is your starting position.
On an exhale, keep your legs extended as you slowly begin to raise your legs up off the ground until they form a 90-degree angle at the hips. It's OK if you're unable to reach a 90-degree angle; go as far as your body allows without pain or straining.
On an inhale, slowly lower your legs, returning to the starting position without letting your feet touch the ground.