Swiss-ball bent-over raise

Works: rear deltoids and rotator-cuff muscles
Sit on a Swiss-ball with a light dumbbell in each hand, with your arms at your sides and palms toward you. Bend forward at the waist until your chest is just over your thighs. Without bending your elbows, squeeze your shoulder blades together and raise the weights until your arms are parallel to the floor. Pause, then slowly lower your arms.
Watch your form: In the top position, your arms should form a straight line from fist to fist.

6. Superman crisscross
Works: lower back and gluteal muscles
Lie facedown with your legs straight and your arms extended past your head. Simultaneously lift your arms, chest, and legs so that only your abdomen and pelvic area are resting on the floor. Holding this position, spread your legs. Pause, then reverse the move to cross your left foot over your right. Repeat, this time crossing your right foot over your left.
Watch your form: Keep your legs as close to the floor as possible without letting them touch it.