Stamina

Stamina effects how long you can sprint and everything that uses your stamina. Using your weapon/sword uses stamina though some weapons use more stamina then others. Stamina regenerates over time, even outside of safe zones.
If you use up all your stamina, you won't be able to sprint or strike with your weapon until your stamina bar surpasses the 'N' in the stamina text on your stamina bar below your health.
The Stamina skill is increased by sprinting.