Endurance of the Berserkers, ArM5, p.134.
Duration is Concentration or until the caster, who is also the target, runs out of fatigue levels. But there's a legacy paragraph from previous editions stating "Consecutive castings delay the end of the spell — that is, put off the time when accumulated wounds take effect — but a body can only take a number of consecutive castings equal to its Size + 2".
This appears an error, since either the caster loses Concentration, in which case the spell ends before he can recast it. or he can just keep concentrating on it without any need of recasting.
Finally, note that the caster acts as unwounded until the spell wears off. In principle, he could take any number of killing wounds, and have them healed before the spell wears off. How this all works should probably be clarified.