Come to a quadruped position: place your hands under your shoulders. Your fingers facing forward. Place your knees under your hips. keeping your spine and neck in a neutral position; you should be looking at the floor.

Slowly extend your left leg behind you while reaching your right arm forward. Slowly return to the starting position and do the move on the opposite side. Lift the leg off the floor until it is at or near parallel to the floor. Keep both shoulders parallel to the floor. Your head should remain aligned with the spine throughout the movement. Do not lift the head or let it sag downward.

Back to starting position, maintaining balance and stability in the shoulders, pelvis, and torso. Alternate sides.

It looks easy, but it´s not. Let´s see the usual mistakes or problems with the next pic.

I have to say this was not on purpose :) Usually, my first set of 30 reps (15 each side) is for stabilizing. Flipped disks are that funny :)

You should not lift your leg above hip height. This will help to avoid upward rotation at the hip. Do not allow the shoulder to tilt upward. If you cross the “red line”, you should adjust instead keep counting wrong reps.