You really can do anything you put your mind to, at least when it comes to creating definition.  A recent study at the University of South Carolina found that when people focus on using a specific body part, (for instance, the biceps during a curl) muscle activity in that area increased by up to 26 percent.  Researchers say this is likely because the brain sends more signals to those tissues, which causes greater number of muscle fibers to fire.  So it’s time to focus and concentrate!