Yes, you have to be strong to put some size on, but not at the cost of sacrificing form and isolation. If you incorporate other muscle groups just to heave the weight up, you're no more than a power lifter. Remember, size comes from isolation and the pump. Go as heavy as possible, but without sacrificing technique and truly go for the pump. When I remind myself of this, I have to drop the weight down a bit. The ego wants to throw up more, but you wind up sore in all the areas except the muscle you were trying to get to grow!