The principle is good, and I guess if you have the right size, it helps. However I am a fine, which puts S, so I took the S, and this time, well impossible to keep the belt over an hour because it compresses me literally. This suggests that in order for an S, it must be more than thin (and pregnant ....) I do not advise buying on the net that you can not test the size that we need .... Very disappointed ....
