Personally, i think that they do. I started training about 5 years ago. I have a friend that i was about 1/2 of an inch taller than. He don't train. These days I'm a half of an inch samaller than him. Ok, shoes etc may come into affect hear, but I'm convinced that they do make you lose height. After every session i always hang from a chin bar for bouts of 30 seconds to stretch out the spine. I don't seem to be shrinking anymore.