I have thick wrists, no fat, just thick, I am not a particularly large person otherwise and none of my three brothers, parents or grandparents have wrists that are anything approaching as big as mine which seems to rule out genetic inheritance, I was however from a very early age on a very keen and frequent kayak canoeist and am inclined to think that my wrists have developed as a consequence of my training regime and diet over many years. I have also developed a more muscular torso than any of my siblings.