Endurance

From LSWiki

  Endurance basically affects how long you last in combat.  How fast your
endurance burns depends on how tiring the weapons are that you are using and
how much effort you are putting into the battle; see 'help effort'.  If you
endurance drops below 0, you will be unable to attack until it rises.  The
higher your recuperation skill, the more quickly you recover lost endurance.