In many styles of Okinawan Karate body conditioning (tanren) is performed. The most prominent, kote aite/ude tanren (foremarm strengthening/conditioning) involves absorbing impact to the forearms, slowly building up resilience over time.
Others include similar procedures to the legs and strikes to other parts of the body. An important point is that the parts of the body that are conditioned are those most likely to receive an impact. For a karate-ka, that area is foremost the forearms, with upper arms and areas of the torso following. Thus, according to the doctrine of Okinawan Karate (and common sense), areas such as the groin, underarms, neck/throat, and such areas are unnecessary and stupid to condition (or try to).
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