When you're short on time, multitasking is mandatory and the stability ball indispensable. It challenges your core while you focus on training other muscle groups. Try the traditional biceps curl while sitting on the stability ball.

Sit on a stability ball (choose one appropriate for your height) with your feet flat on the floor and your toes facing forward. With your shoulders back and down, torso erect and abdominals tight, hold a dumbbell in each hand with your palms facing upward. With your elbows tight against your body, extend your arms toward the floor.

Exhale as you curl up the dumbbells toward your shoulder, stopping at the point your biceps are fully contracted. Pause, then inhale as you lower the dumbbells to the starting position. Concentrate on slowly controlling the lowering portion of the exercise.

Key points: Keep your elbows against your body and your wrists strong throughout the exercise. Try 12 to 15 reps with a challenging weight.