Medieval ? Not that I can think of. But Ancient ? Yes, kinda. Meet the Gastraphetes, or “belly bow”. While the wiki page depicts one way to reload it, I remember reading about users who would lie on their backs, brace the bow with their feet and pull the string back with their hands and shoot it that way - only as defenders in a siege though, but then one would think lying down in open battle seems a little bit dangerous :).
Can’t find that cite any more though 