Stamina

Stamina is a feature in Halo 3: ODST. When the player starts to take damage, their stamina will start to decrease. When it is getting low, it starts to flash red until the player's stamina is gone, in which case, their health will start to be affected and decrease as well. However, stamina can be recovered if the player takes cover and stops taking any damage.

Trivia

 * The sound files that are heard when your stamina is changing (regenerating, low, etc.) are actually replacements for the energy shield sound effects and not dialogue. These include panting (stamina low), a deep breath (stamina recharging), etc. These appear to be similar to what would happen if you run out of stamina. Note that the sound effects pertaining to your current health are different, since you will hear a beeping sound getting faster as your health goes down. These beeping sounds likely correspond to the pulse of the afflicted individual, or are in place to represent a pulse.
 * The Stamina serves as a replacement for the Energy Shield.
 * Some strengths and weaknesses from the Energy Shield seem to be retained; plasma weapons seem to be slightly more effective on you rather than Brute projectile weapons (usually the spiker), plasma pistol overcharges seem to drain most if not all of your stamina, and Brutes will sometimes deploy a Power Drain which affects your stamina.