Cheating
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In general, doing exercises with proper form is going to give you the best results. When you're working out, try to focus on quality, not quantity. "If you have to cheat or break form to get another rep or two in, those additional reps are not nearly as beneficial as you think," says Kaeding. Bad form is a sign that you've probably reached your limit and continuing to exercise beyond that makes it more likely that you'll injure yourself.