...and shoulders...and abs.

Underhand bent-over row: Any row can give you a great upper-body workout, but this variation is all about the biceps. The reverse grip isolates your biceps, strengthening them more than a neutral or overhand grip can. Plus, you'll feel your shoulders become more sculpted with each rep. 

A) Grab a pair of dumbbells, bend at your hips and knees, and lower your torso until it's almost parallel to the floor. Hold the dumbbells at arm's length, palms facing forward.

B) Keep your elbows next to your sides as you row the weights to your sides. Pause, then slowly lower back to start. That's one reps.