Adamantium Skeleton

Adamantium Skeleton is a Fallout 3 Perk.

With the Adamantium Skeleton perk, your limbs only receive 50% of the damage they normally would.

Trivia
This perk pays homage to Marvel Comics superhero Wolverine and his Adamantium-laced skeleton. Bethesda previously made a less obvious reference to Marvel's indestructible fictional metal with the Adamantium Armor found in The Elder Scrolls III: Morrowind Tribunal expansion pack.

Note that this perk does not reduce how much HP is lost when you're hit, but it increases how much damage the limbs can take before becoming crippled.