5. The faux pas
Lifting the wrong amount of weight

The facts If you lift weights that are too light, you won't see improvements in strength, tone or bone density. If you lift weights that are too heavy, you'll compromise proper form, increasing your injury risk. You'll also be forced to recruit additional muscles, for instance, using your entire body to complete a biceps curl, thus cheating the targeted muscles of a good workout.

The fix For the most significant strength building, perform 4-6 repetitions per set; for more moderate strength building, perform 8-12 repetitions per set, choosing weights heavy enough that you struggle through your final few reps, but not so heavy that your form falls apart. If you get to your final rep and feel that you could perform another one, increase the weight by 5-10 percent. You may find that when you've considerably increased the amount of weight you're using, you'll drop to fewer reps, which is fine, as long as your targeted muscles are fatigued by the final rep. Don't worry: Lifting to fatigue will not leave you with monstrous muscles.