Hand conditioning, the hardening and callusing of the hands, is not appropriate for sport or self-defense karate or jujitsu; it is irrelevant to judo.
In sport karate, players do not make contact or they wear gloves.
In contest where contact is prohibited by the rules, players who have conditioned hands are required to wear bandages to minimize the possibility of injury if acci- dental contact is made.
In matches where contact is permitted, the players use padded gloves. A karate contestant who had spent years in hand conditioning would not be allowed to hit the opponent player with his hand weapon.
Sport judo rules forbid striking the opponent player with hand or foot blows.
For practical self-defense it is neither desirable nor necessary to condition your hands. Hand conditioning was an appropriate feature of ancient karate training. Because it was sometimes necessary to break through the wooden armor of the Samurai soldier, karate fighters
in feudal times were required to spend years of effort to callus and desensitize their hands and feet so that they could deliver forceful blows to hard surfaces with- out feeling pain.
Today there is no reason to strike at hard surfaces in a manner which would hurt your normal, unconditioned hand. With an understanding of appropriate body target areas, you can avoid striking at hard, bony areas such as the collarbone (clavicle). When you do strike at a bony structure, such as the knee or the bridge of the nose, you can hit with appropriately forceful blows
without hurting yourself. A kick into the knee does not require conditioning; hitting with the side of the closed fist onto the nose delivers enough force for self-defense use.
Heavy conditioning can cause permanent injury to your hands and it can seriously impair manual dexterity.
Extreme hand conditioning is irreversible. The ability to do skillful, intricate work might be seriously reduced.
If a job requires contact with the public, the misshapen appearance of conditioned hands could be an impediment to employment.
Heavy conditioning implies willingness to fight. Should you need to defend yourself on the street, you might
have difficulty persuading the law that you were defending yourself; the evidence of conditioned hands would suggest preparation for fighting.
Hand conditioning is necessary if you want to do stunts and tricks such as breaking bricks without hurting your- self. If you really feel that it is important to show off in such a manner, you will have to work at long-term hand conditioning. Be aware that once you have heavily conditioned hands, you are risking the chance that they will never again be normal. It is a heavy price to pay
for doing a stunt.