I recall reading a short story in which a prisoner meets several physically enhanced gladiators (or possibly, long-term prisoners in some survival-type prison).
Specifically, one of them had a triple jointed arm that (she?) could crack like a whip, and knuckles that could dent steel. The other arm was double jointed and might have been outfitted with a blade.
This would have been from the golden age of science fiction, not anything recent.