This exercise from E! host Maria Menounos’ circuit routine not only tones the backs of your arms, it also engages your core.

Here's how to do it: Lie face up with your feet on the floor, knees bent, and a 5-pound dumbbell in each hand. Extend your arms up, palms facing in. Hinging your elbows, lower the dumbbells until your arms form backward L's (a 90° angle). Raise your arms back overhead. Do 10 reps.

Try this move: Close-Grip Triceps Press

Have more time for a full workout? You can do this exercise as part of a fat-melting circuit. Watch Maria Menounos, author of Every Girl’s Guide to Diet and Fitness ($14, amazon.com), show you how to do a speedy, 7-move exercise routine. Do the circuit two to three times to get a great workout in less than 20 minutes.