Astronauts on the Space Shuttle and International Space Station could wear a padded belt to relieve lower back discomfort. Some reported such discomfort while strapped in their seats (on their backs) during the wait for launch, and others felt it as their spinal column expanded in weightlessness.
NASA transferred this and many other crew equipment items to the Museum after the Space Shuttle program ended in 2012.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.