As a personal trainer for pro athletes, actors and Fortune 500 execs, I’ve been in a lot of gyms in my life. As you can imagine, I’ve seen a ton of training mistakes. Standing out among the many are the following ten egregious—and sometimes dangerous—progress killers. (In addition to squatting too deeply, the guy above is making nos. 3 and 9.) If you really want to build the body of your dreams, avoid them like the Shake Weight.