The next time you head to the gym for a strength-training session, be sure to keep this tip in mind. No matter what your circuit or how heavy your weights, your goal for each session is to feel that shaky, uncomfortable burn. Why? Because each session should be challenging your muscles; that uncomfortable feeling means that you're building up those important muscle fibers. Since more muscle equals faster metabolism, don't shy away from feeling the burn — embrace it! Pin or print this poster to help you remember to push yourself.