When you're working out, you want to make sure you're working out all of your body parts evenly. When you're working out opposite parts, say your thighs and your hamstrings, your chest and your back, or your biceps and triceps; they're opposite muscle groups. Working them out at one time, saves time, but also gives you a really nice, even development. For this edition of Tone Up, Marcie Fraser works her biceps and triceps at the same time, with hammer curls.