You are capable of legendary feats of stamina.
Prerequisites: Con 25, Endurance.
Benefit: Whenever the character makes a check for performing a physical action that extends over a period of time (running, swimming, holding one’s breath, and so on), he or she gets a +10 bonus on the check.
Source: Standard Reference Document under Open Game License v1.0a, which updated this feat originally published in the Epic Level Handbook, page 54.