>8. Triceps kickback
The faux pas Swinging your upper arm, dropping your opposite shoulder, trying to lift your arm and the weight too high behind you
The facts When you make any of these mistakes, your triceps aren't sufficiently challenged, and you also may place stress on your shoulder and elbow joints.

The fix Hold a dumbbell in your right hand and stand to the right of the long side of a bench, feet hip-width apart or in a staggered stance. (You also can kneel on the bench with your left knee.) Flex forward at hips at about 90 degrees, and place left hand on bench for support. Keeping torso stationary, bend right elbow so upper arm is parallel to ground and forearm is perpendicular to ground, palm facing in. Position elbow close to waist and contract abs. Keeping upper arm still, use triceps to straighten arm behind you until end of dumbbell points down (shown). Slowly bend elbow to return to perpendicular position. Strengthens triceps.