Adrenaline

Certain Warrior skills are fueled by adrenaline rather than Energy. It is gradually built up each time the Warrior hits or is struck in combat, each such blow being added to the characters adrenaline level. Some skills increase the rate of adrenaline build up, while others expend it entirely.

Adrenaline is not actually gained in strikes, but in points. You gain 25 adrenaline points for succesfully attacking and by taking damage you gain 1 point of adrenaline for every 1% health lost from your maximum. Commonly 4 strike skills are charged in about 3 hits time, because you take some damage at the same time. See this table for approximate number of adrenaline points needed for skills.

1Sever Artery and Counter Blow are 4 strike skills, but they actually need about 100 adrenaline points.

The Monk Enchantment Balthazar's Spirit will allow a target ally (or yourself) to gain adrenaline and energy when taking damage. Similarily, the Warrior skill Wary Stance will allow the Warrior to gain adrenaline while blocking attacks against him.

Other Warrior skills increase adrenaline gain; for example Berserker Stance and "To the limit!". These skills will allow a player to build up adrenaline quickly at the initiation of combat (Berserker Stance), or gain an extra adrenaline boost during combat. The shout "For Great Justice!" is slightly different in that it shortens the recharge delay of adrenaline skills rather than increase adrenaline gain.

Reference
Research done by Ensign and Silmor. Original GW Guru thread.