Skyrim:Stamina

Stamina is your character's physical energy, and is used to perform various strenuous activities, in particular power attacks, bashing with a shield, sprinting, rolling while sneaking, and zooming in with a bow. If your stamina is completely depleted, you will be unable to perform these strenuous activities. Unlike magicka, your character can perform any action that has a stamina cost as long as it has at least one point of stamina available. Stamina is comparable to "Fatigue" in earlier Elder Scrolls games.

Some dragon shouts such as Whirlwind Sprint also use a small amount of stamina. However, this isn't a huge problem, since by the time you are able to shout again, your stamina will have fully restored.

Current Stamina

You may inspect current stamina in Skills menu.

Increasing Stamina
The amount of stamina you have depends on your character's level. Each time you level up, you can choose to add ten points to your stamina, or to another attribute. Adding to your base stamina when you level up increases your carry weight by 5. You can temporarily fortify your stamina using magical effects as detailed here. Temporary changes to your stamina (such as damage, drain, or fortify) do not affect your carry weight.

Restoring Stamina
The green bar in the bottom right of the screen shows you the current status of your stamina (although this bar will be invisible when stamina is full). Stamina can be restored in several ways:
Stamina regenerates whenever you are not doing an action that uses stamina. You regenerate 5.00% of your maximum stamina per second outside of combat and 1.75% inside combat.
As a result, sleeping or waiting fully restores your stamina.
Restore Stamina effects are available in various forms:
From potions that can be found or purchased
From custom potions
Some types of food restore stamina
From spells that restore health, which restore stamina with the Respite perk
Whenever your character levels up, your stamina, health, and magicka are fully restored.

Unlimited Stamina
Unlike spells, which cannot be cast if you do not have sufficient magicka, Skyrim allows players to perform actions that require more stamina than they have. When you perform an action under such circumstances, a timer is set based on your stamina deficit and your stamina regeneration rate at the moment you perform the action. When the timer reaches 0, your stamina will start to regenerate again. However, Skyrim has a maximum amount of time coded into the game before the timer immediately resets. This is governed by the fStaminaRegenDelayMax game setting in the Creation Kit, which is set to 5 (seconds) by default. Items such as potions or food that restore stamina (by an absolute amount) immediately reset the timer then restore the specified amount. If they instead increase regeneration rate by a percent, they will reduce the timer only if used before actions, but will increase the regeneration rate after the timer reaches 0 regardless of the timing. This effectively means items with a continous restore stamina effect will grant you unlimited stamina during its duration.

A few simple examples illustrate the above mechanics. Consider a player that regenerates 10 stamina per second and whose power attack consumes 80 stamina.

Case 1: the player is at 80 stamina. He/she performs a power attack which depletes his/her stamina. The stamina bar immediately begins to fill.
Case 2: the player is at 50 stamina. He/she performs a power attack which depletes his/her stamina and set the timer to 3 seconds. After 3 seconds, the stamina bar begins to fill.
Case 3: the player is at 10 stamina. He/she performs a power attack which depletes his/her stamina and set the timer to 7 seconds. After 5 seconds, the timer reaches 2 seconds. Because fStaminaRegenDelayMax = 5, the timer immediately resets and the stamina bar begins to fill.
Case 4: the player is at 10 stamina. He/she performs a power attack which depletes his/her stamina and set the timer to 7 seconds. He/she immediately drinks a potion that restores his/her stamina by 15 per second for 5 seconds. The timer immediately resets the moment he/she drinks the potion and the stamina bar begins to fill. For the next 5 seconds, he/she can perform as many power attacks as he/she wants, since every time the potion effect ticks, the timer is reset and he/she will have positive stamina.

NPC Stamina
All NPCs and creatures also have stamina, which is calculated differently than the player's stamina. Their stamina is summed from three separate contributions:
The race provides a starting stamina.  
Individual NPCs and creatures can have a fixed stamina adjustment.
For most NPCs and creatures the class provides an additional 0-10 stamina points per level.
The rate at which enemies regenerate stamina is determined by their race.

Notes
Frost damage drains stamina.
Unlike in previous Elder Scrolls games, jumping does not reduce your stamina, nor does walking or running affect the rate of regeneration.
When your stamina reaches zero, the stamina bar will flash green. It will never take more than 5 seconds before it starts to refill again.