Your ability to curl a weight is determined by the distance of the weight (palm) from the point of the fulcrum (elbow). Your curling strength is increased or decreased by the square of the distance from the palm to the elbow.
Let me plug in some figures to help you visualize what I’m saying. Let’s suppose you’re curling 100 pounds. Further, let’s suppose the distance from your elbow to your palm is 12 inches. The force required to lift the weight is 100 times 12 squared, or 100 times 144, which equals 14,400 pounds of force. Now curling the wrist can reduce that force.
Let’s suppose that by curling your wrists you can reduce the distance from 12 to 10 inches. You now have 100 times 10 squared, or 10,000 pounds. You’ve reduced the force by more than 30 percent even though you’ve only reduced the distance by a little more than 10 percent. So, if you can curl your wrists, you can go deep into the movement with a heavier weight. To do that you need raw power in your forearms’power that can curl wrists holding weights that even biceps cannot handle.
The answer is to place as much emphasis on forearm development as you do on biceps growth.
‘Larry Scott, Loaded Guns