It won't be good, because if you pull the spine in the opposite direction, if the abdominal muscles are not very strong, the pressure will be on the spine. It is recommended to stay on the floor or in a hard bed. You'd better not let others crush your feet. Didn't you find that part of the force of pressing the foot was distributed to the leg? If you want to practice your waist specially, you should control your feet and don't lift them. ...