The prone cobra is a back extension exercise performed off the floor. You do not need any equipment to do it, and so there are no excuses. It works all the muscles along the back of the body, but notably the lower and upper back muscles. The way the exercise is performed here with the thumbs turned backwards also works the external rotator cuff muscles of the shoulder, which can become weak through hours spent holding the bars. This exercise will help you stand up straighter with your shoulders back.
Because this exercise is a ‘postural exercise’ it is best performed with progressively prolonged isometric holds. As you develop more endurance in these muscles you can increase the duration of the held position and reduce the rest in between. As an ultimate goal you should aim for three minutes work in total, broken down into progressively longer holds with fewer ‘sets’.