Hehe, get your mind out of the gutter. Karate IS a contact sport. One of the "exercises" we used to do to toughen the inner side of our forearms was to stand facing another student and swing and hit our inner forearms together. Sensei Kise would often walk walk down a row between us hitting our arms and wrists with his instead. You'd be surprised how much that can hurt, swing your arm hard and hit a steel pole with your inner forearm, you'll get the idea.
