Inversion tables allow users to hang upside down from their feet. The experience changes body mechanics—stretching and relaxing muscles and even temporarily increasing the distance between vertebrae, says Roger Teeter, founder and chairman of STL International Inc. of Puyallup, Wash., which does business as Teeter and sells tables in the U.S. and Canada. Some people get dizzy, particularly if they are new to inverting or if they come up too fast, he adds.