A very obvious physical phenomenon and you might laughed at this is aikidokas have hairy wrist. I am of Asiatic and Spanish origin, and my family and relatives are not hairy or have hairy wrist. I have noticed that aikidokas that trained the longest have hairier wrists (even the ladies in the dojo).
I spoke to my human anatomy and physiology professor at the university of Sydney and he could not explain it. His wild guess was because we (aikidokas) get grabbed at the wrist more frequently than the average person, the circulation around the are is better, hence it stimulates the growth of hair. But he could not explain why that same theory does not work on bald headed men.
I spoke to my Shiatsu practioner (which is also a accupuncture practioner) and her explaination was because there are a lot of exchange in ki at that point coming from differrent people and hence sources, the life force stimulates the growth of hair, the life force stimulates and revitalizes that point, hence good and solid bones, stonger muscles, flexible and thick joints. The exchange of ki is so strong that one can issolate the area visually.
I guess the latter explaination is good news to the power of ki extention, but it just leaves us aikidokas with a cosmetic problem. Bloody Hairy wrists.