You won't believe how difficult it is to perform this one-sided chest strengthener on a roller. It may look easy to move one arm at a time, but try it -- you'll discover the core has to really work to hold your balance.
1. Hold a dumbbell in your right hand and lie down on a full-length, round roller with your head and hips supported on the roller (you can place a yoga block behind your head if necessary). Straighten your right leg out in front of you and rest your left arm alongside your body with your hand close to your hips. Raise your right arm directly above your right shoulder, palm turned away from your face. Keep your abdominals pulled in but maintain the natural curves in your lower back and at the base of the neck.
2. Inhale, and slowly move your right arm out to the side and down to shoulder level. Focus your eyes up at the ceiling and concentrate on keeping your hips and shoulders motionless as you lower your arm. The tendency is to roll your hips off to the right, but if you contract your core muscles, you can keep your hips and shoulders level. Pause at the bottom, then reverse directions and return to the start position. Repeat 12 times, then perform this exercise on the other side.
Karen Voight is the creator of a line of fitness DVDs, including "Sleek Essentials."