Bring your elbows close together as you pull the cable handles inward.
The butterfly exercise, also referred to as the pec deck fly, is an isolation exercise that targets your pectoral muscles. Besides toning your chest, it helps strengthen your bones and improve balance and posture. The exercise can also help decrease or prevent back pain or injury. Consult your doctor before trying the butterfly exercise, especially if you have a prior chest or back injury.
For best results, always practice proper form when doing the butterfly exercise. Sit up straight on a bench or chair, your back facing a cable machine. Grasp the cable handles and bend your elbows into 90-degree angles out to your sides. Your upper arms should be parallel to the ground at chest-height. Pull the cable handles together in an arc until your elbows almost touch in front of your chest. Repeat for a total of 12 repetitions. To be sure you are really targeting your chest, squeeze and contract your pectoral muscles for two seconds when you pull the cables inward.
If it's more comfortable, stand while doing cable butterfly exercises. Use dumbbells, an exercise band or pulleys if you don't have access to cables. You can also use a pec deck machine if one is available at your local gym. To boost the intensity, sit on an exercise ball while you do butterflies. This forces you to use the muscles in your abdominals, back and waist in order to remain balanced and upright.
Do not push with your hands when you bring the cable handles together, which lessens the intensity of the exercise. Instead, always pull your elbows together. Perform all movements slowly and with control. This will not only help prevent injury, it will recruit as many muscle fibers as possible. Keep your arms locked into position throughout the entire routine -- do not straighten your elbows or move your arms up and down.
Keep your back in a neutral position while you do the butterfly exercise. Never lean your torso forward as you squeeze the cables together. This puts stress on your back and can lead to injury and pain. Do not move in an uncontrolled manner or jerk the cables at any point. Always work at your own pace. Start out with just a few repetitions if needed and work your way up to the full amount.