When the left analog stick is pushed down, you will sprint. Sprinting increases your speed for a short time. Improved Sprint Recovery (1) shortens the wait time between sprints, while Increased Endurance (2) increases the maximum time allowed sprinting. To fully maximize your speed, after sprinting wait until your character stops breathing audibly, then resume sprinting
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Sprinting will reveal you on radar, even if you have Improved Stealth (2), This can make it very easy to kill enemies near their spawn point even without motion sensors, because they will be eager to enter the fray again and sprint, revealing their position.