From D&D Wiki
|This material is published under the OGL|
You expend some of your rage to strike your opponents with a more powerful weapon blow.
Prerequisites: Str 13, rage class feature, Power Attack, base attack bonus +12.
Benefit: While raging and using Power Attack, you can spend 3 additional rounds of your rage as a swift action to add your Constitution bonus on damage rolls for melee attacks or thrown weapon attacks you make on your turn. If you are using the weapon two-handed, instead add 1-1/2 times your Constitution bonus. This bonus damage is not multiplied on a critical hit.