Standing-Calf-Raise MachineWhy it's bad: Most men can handle a substantial amount of weight--often more than they can squat--when doing this exercise because of the small range of motion of the calf raise. This adds up to a lot of unnecessary spinal compression, which can lead to severe back problems.
Smith Machine (for squats)Why it's bad: The path the bar follows doesn't allow for proper spine mechanics, which can place excessive stress on the lower back. That's because the natural movement of your body during a squat is an arc, not straight up and down. Stick with the free-weight version.
Pec DeckWhy it's bad: It forces you to abduct your upper arm horizontally--that is, move it away from your body while holding it parallel to the floor--while rotating it backward against a heavy weight. This places tremendous stress on the front portion of your deltoid, which can lead to nerve injuries.