It's hard not to believe it's true when you see the picture of his arm. It looks boney, thin and atrophied. His name is Amar Bharati, and he's an Indian holy man that claims he's kept his right arm raised since 1973.
He was a middle-class man up until 1970, when he decided to quit his wife, kids and job to become a holy man in service of Shiva. After 3 years, he decided that he was still too attached to earthly pleasures, so he raised his right arm as a way to separate himself from the world. Other people also say he raised his arm as a call for peace.
Bharati says that he endured a lot of pain in the beginning, but not anymore. This is probably because his body adapted to the position, locking it into the angle that the arm is at. I can't imagine keeping my arm raised like that for more than a few minutes, much less 39 years. How long could you last?