Y'ffre's Endurance was added in Update 6, when it replaced Vigor (no relation to the Assaultskill of the same name), which had a lower value Stamina recovery effect. Vigor remained as a Redguard skill after Update 6, and was renamed Exhilaration, currently known as Martial Training. Update 21 changed the bonus from percentage-based to flat values, and changed the level requirements from 5, 15, and 30 to 10, 20, and 40.
Y'ffre's Endurance: The Wood Elf racial skill Exhilaration (formerly Vigor) has been replaced with Y'ffre's Endurance, which grants an increase of 7%/14%/21% to Stamina Regeneration while in combat.