The splits!
Mind you, I am not in as bad of shape as many my age, but I have become lazy. I don't know any other fifty year olds who can side kick over their heads, but my range of motion has decreased in the past few years.
Today, I slipped a little, went a bit out of control and my legs split apart. My hip dislocated and it hurt like a mother fucker.
It went right back in, but now, I am sore.