Assume a push-up position, with your body at roughly 45-degree angle in relation to the floor. Curl your hands into fists and rest your body weight on the larger knuckles of your index and middle fingers. Lower your body until your chest is parallel to the ground. Push down on your knuckles until your body returns to its original position. For more follow http://www.ehow.co.uk/how_8480497_make-knuckles-harder.html.