Walking into the gym and expecting a great workout is like walking into the supermarket and expecting a gourmet meal. The basic ingredients are there, but like they say in the infomercials, results may vary. With working out, as with cooking, a little bit of smarts, dedication, creativity and knowledge will make all the difference between perfect pasta and a gelatinous ball of mush.

For this list of no-no exercises, we consulted Stuart McGill, PhD, professor of spine biomechanics at the University of Waterloo, in Ontario; Nicholas DiNubile, MD, author of FrameWork: Your 7-Step Program for Healthy Muscles, Bones, and Joints; and trainer Vern Gambetta, author of Athletic Development: The Art & Science of Functional Sports Conditioning.

Here are the exercise machines you must avoid: