You are considered extreme even among other barbaric warriors, and you enter a deeper state of rage than others. Goliath barbarians favor this feat.
Prerequisites: Con 13, rage ability.
Benefit: Whenever you activate your rage ability, you take an additional –2 penalty to your Armor Class, but you gain an additional +2 bonus to Strength and Constitution. These bonuses and penalties stack with the effects of rage, greater rage, and mighty rage.
Source: Races of Stone, page 143.