Axis at elbow 5.0 cm Time to pump it up baby! When you do a curl like a weightlifter, your bicep muscle shortens and this applies a force to your lower arm. Because of the elbow acting like a hinge, this force acts like a Q! or said another way a force which causes rotation. There are several things which can affect how much you can curl. Obviously, if you are stronger, you can curl more. But, for the same muscle strength. if you moved the tendon attachment (toward or away) [ ] {y from the elbow. you could curl more too