The physical side of a literary hero is almost always near superhuman. In Homer's "Iliad," Achilles is unstoppable as he fights the Trojan forces, rendered mortal only by his vulnerable heel. Odysseus, likewise, in "The Odyssey" devotes superhuman resolve and fortitude to getting home to his wife and kingdom -- except for his romantic dalliances on the way. It is in their physical strength that heroes such as these match our modern comic book superbeings, but the resemblance ends there; both Odysseus and Achilles reveal deep moral flaws that overwhelm their physical strengths.
The second characteristic of a literary hero's anatomy is his morally flawed nature; the Achilles/Odysseus characteristic of hubris, or god-defying pride, threatens to destroy these characters. Such hubris is also found in Beowulf, the Anglo-Saxon daredevil who slays several monsters to gain a restless reign over an unstable kingdom, and it is found in Shakespeare's heroic protagonists such as Othello and Macbeth, warriors of great physical prowess who are destroyed by their darker natures. These men, killing machines for their countries, are fraught with jealousies, dark motives and unwholesome ambitions.
One salient characteristic of a literary hero's anatomy that places him above ordinary protagonists is his concern for his own kingdom and culture. Beowulf, Odysseus and Othello all desire, and fight for, the greater good that will improve the kingdoms they reign. It is this "social worker with a dream" aspect that separates literary heroes from mere treasure hunters and swashbucklers; this characteristic is most strongly reflected in later, less blatantly heroic protagonists such as Pip in Dickens' "Great Expectations" and Jonathan Swift's Lemuel Gulliver.
Part of a literary hero's anatomy that fuses his physicality, his moral flaws and his desire for the greater good is his cathartic nature, described in Aristotle's "Poetics." Unlike Superman or Indiana Jones, the literary hero usually dies, but the catharsis of his death is an emotional release for the reader. Beowulf, Achilles, Othello and Macbeth all face their deaths bravely and philosophically; perhaps a character cannot really do that well until he has the strength and moral fortitude of a literary hero.