The stamina stat is an attribute that adds to the base health maximum of 100% in Strife. It starts at zero and has a maximum value of 100, giving the player a maximum health value of 200%. The additional health makes using the Sigil more viable, especially as it consumes more health with each Sigil piece. The surgery kit's effectiveness also increases with higher stamina, since each kit will heal the user up to their maximum health.
The stamina stat also increases the damage inflicted by the punch dagger, allowing it to kill stronger enemies with fewer hits - with enough stamina it becomes possible to gib acolytes with a single blow. This makes the punch dagger a more useful weapon as the game progresses, especially in situations where stealth is preferable to force.
In the early stages of Strife, stamina upgrades are received from Gerard in exchange for stamina implant tokens received from Macil; later in the game, stamina upgrades are given to the player immediately on completing certain objectives, saving them the trouble of returning to The Front. Each upgrade increases the stamina stat by 10, thus increasing the player's maximum health by 10%.