Performing knuckle pushups can build callouses and thicken the skin over your knuckles due to the pressure and friction absorbed as they're pressed against the training surface. The exercise also strengthens your wrists, chest, triceps and shoulder muscles. Assume a standard pushup position, face down on the floor, with your feet together and body straight from head to feet. Instead of laying your palms on the floor, make fists and place them on your surface with your palms facing each other. Keep your body straight as you lower your chest to the floor and then rise to the starting position. You can twist your hands just a bit to add more friction, which will help build the callouses you seek. Perform knuckle pushups a bit slower than standard pushups, as your fists provide a less stable base than flat palms. Placing your hands on a thin mat, carpet or a towel may help to prevent hand injuries.
Hitting Bags or Pads
Other methods of creating callouses and training your knuckles include punching a heavy bag or hitting focus pads held by a training partner. Wear boxing hand wraps while hitting the bag or the pads, to help protect the small bones in your hands from sustaining injuries. Begin with single, moderate-intensity punches and gradually work up to throwing combinations with full power.