A 30-minute workout that focuses on your upper body — arms, shoulders, back and chest — and core. Keli Roberts instructs.

Intermediate exercisers. This workout is fast-paced in places and often challenging. You will need one or two sets of dumbbells (3 to 8 pounds), a medicine ball (not too heavy - maybe 4 pounds), and a mat.

I'll never figure out what got into me the day I brought home a 6-pound medicine ball. It's been the bane of my existence ever since. I struggle through exercise DVDs that wouldn't be that tough if I'd bought one more appropriate for my level of fitness, say, 4 pounds or less. Fortunately for me and this workout, Keli Roberts used the medicine ball as more of a balancing and core-strengthening tool, and only utilized it as a weight-bearing item a couple of times. Roberts has you performing a variety of exercises, alternating between the dumbbells and medicine ball. The dumbbell moves are classics, like bent over rows and clean and press, and occasionally she'll throw in a surprise, such as doing biceps curls while standing on one leg. After a couple of dumbbell exercises, you hit the mat for upper body and stabilization exercises — push ups with one hand on the medicine ball, plank with your feet on the medicine ball and the like. These are not easy moves, and Roberts has you moving at a brisk pace (her cueing is excellent, so as long as you're an experienced exerciser, you won't get lost). My heavy medicine ball did cause a couple of problems — it moved sluggishly from hand to hand during one push-up sequence and I fatigued quickly when it was used for its weight. And although they said you would need one pair of dumbbells, I required a couple pairs — the weight that was right for my rhomboids was far too light for bent over rows, even with both dumbbells in one hand. My only real complaint is that there wasn't enough triceps work, so I added a few kickbacks at the end. But overall, this is a highly effective workout — triceps aside, I fatigued just about every part of my upper body and core. And you know what? I was tired and a little sore at the end, but I swear that medicine ball felt a little lighter when I picked it up to put it away.