If losing weight is on your list for 2009, cardio will help burn calories, but you also need to strength train to achieve muscle definition and prevent injury. Lifting weights can be difficult for people who aren't used to the intense sensations of fatigue and burning that arise in their muscles, but these feelings are completely normal and necessary if you want to strengthen and tone. So instead of stopping the moment you begin to feel uncomfortable, keep going for another one to five repetitions. Embrace the physical sensations, focus on breathing deeply, and push yourself a little bit further. Afterward, you'll feel proud that you stuck it through, and soon will notice your body is stronger and more lean — two rewards in one.