To perform curl bar curls grip the bar using a narrower than shoulder width grip. There is really only one grip you can use when your hands are narrower than shoulder width on a curl bar. Curl the bar upwards making sure you keep tension on your biceps throughout the whole movement. Lower the weight down in a controlled slower manner.

 

Use your body's natural motion during this exercise, meaning do not be too strict or rigid on your form. Work with your body's mechanics instead of against it.