Question 080: Breaking

My question concerns two particular breaking techniques; hammer fist downward strike and horizontal knife hand strike. First, let me say that I am probably the strongest person in our class, but to brag but to help explain what is happening. In my first test of breaking using a hammer fist, I was unsuccessful in three tries to break hit 3 - ¾" pine boards. I knocked the boards from the holder's hands onto the floor and ended up with a big bruise on my wrist. I am having the same problem when using the knife hand strike. Does this occur because the holders are allowing the boards to move with my strike resulting in my injuries, or is it a technique problem?