Zero gravity chairs are based on NASA’s research into reducing stress on astronauts’ bodies during takeoff, and its concept of a neutral body posture (NBP), the natural posture that astronauts assume in a microgravity environment such as a spaceship. You can use zero gravity chairs in a range of positions, from upright to reclined. But the purpose of the zero gravity chair is to allow you to recline with your feet above your heart, rather than lying flat, as on a bed, massage table, or floor. Bear in mind that lightweight portable zero gravity chairs can fold up flat for easy storage.