Stamina

Stamina measures the ability to sustain physical effort. Stamina is required for attacking, blocking, kicking, jumping, sprinting, and swimming and is represented by the yellow bar. The stamina cost to attack with a weapon is displayed on the weapon's tooltip. When out of stamina, the character cannot do medium or strong attacks.

Each point in strength provides .6 stamina.
Each point in constitution provides 1.2 stamina.

"Stamina management" is the art of not running out of stamina too quickly in a fight, and is regarded as one of the top skills players must learn.

Stamina Drain Modifier

The stamina drain modifier is the rate what which stamina is depleted. Each piece of equipped armor has a stamina drain modifier that impacts overall stamina drain. Heavy armor drains stamina much faster than light or medium armor. Mixing armor types, investing in constitution, and putting points into abilities such as Athlete, Breath Control, Finesse, and Veteran can alleviate high stamina drain problems.

Stamina Regeneration

Stamina regeneration measures the rate stamina is regained every second. All three attribute contribute to stamina regeneration at different rates.

1 Strength = .02 stamina regen per second
1 Constitution = .04 stamina regen per second
1 Dexterity = .05 stamina regen per second

There are many consumables including beer and potions that increase stamina or stamina regeneration.