Which benefits do Extreme Endurance bestow?

Question

The Martial Artist archetype from Ultimate Combat gains an ability named Extreme Endurance at fifth level. I quote:

At 5th level, a martial artist gains immunity to fatigue. At 10th level, he also gains immunity to exhaustion. At 15th level, he gains immunity to stunning. At 20th level, he gains immunity to death effects and energy drain. This ability replaces purity of body, diamond body, and perfect self.

Does this mean that a 5th level MA can do a never ending forced march, provided he has food and water? For how long can a 5th (or 10th) level MA run? Does immunity to fatigue/exhaustion offset the need for sleep?

Any insight, as close as possible to the RAW, appreciated.

As a bonus, any thoughts on which negative effects Extreme Endurance (up to level 10) is designed to alleviate would be useful? I can see it working well with barbarians rage, but apart from that?

Answer 1

Continued forced march or hustling deals non-lethal damage if you fail the required constitution check. Normally, receiving non-lethal damage this way would cause you to become fatigued, which would be prevented by extreme endurance. This would not, however, prevent the non-lethal damage from piling up and eventually putting you out of commission.

As for rules about sleep deprivation, this answer contains this link to the SRD that points to a rule introduced in an adventure path that gives cumulative penalties due lack of sleep. This is the closest thing to RAW that I can find about it, as the source books are pretty ambiguous about the issue and the only (official) consequences of skipping rest is that you do not receive the several benefits of resting.

As requested in comments, I have compiled a list of things that would be prevented by extreme endurance in the level 5 and in level 10:

After level 5, extreme endurance prevents you to become fatigued. This covers exhausting physical activity, as noted before, the aftereffects of barbarian rage, and certain spells and special abilities (a example here, the complete list is way longer). Note that extreme endurance only protects you from fatigue, and damage and all other negative effects that come alongside the fatigued status apply as normal. Also, this incidentally protects you from becoming exhausted due fatigue stacking (doing something that gives you the fatigue status while already fatigued). Also note that even if you manage to get yourself exhausted without being fatigued before, resting for 1 hour removes the exhausted condition and gives you the fatigued condition instead, which is rendered null and void by extreme endurance.

After level 10, extreme endurance prevents you to become exhausted. As the more usual way of acquiring this state is already covered by the level 5 version, this really limits the usefulness of the level 10 version, as its only real use is to prevent the effects of the few spells and special abilities that bestow that state directly (like this and this). As before, you are only protected from exhausted and fatigued status caused by those abilities, other effects will still affect you.

Answer 2

Although it's not casting spells by any means there are some

Spiffy Things to Do If Immune to Fatigue and Exhaustion

Note that immunity also means that a "creature that is immune does not suffer from... any secondary effects that are triggered due to an immune effect." So anytime an effect says because of fatigue something happens or because of exhaustion something happens, the DM may rule that immunity to fatigue or exhaustion, respectively, negates those effects. As an aside, the full-round action Run has entirely independent mechanics that ignore the conditions fatigued and exhausted.

Immunity to Fatigue

Besides being immune to the condition fatigued when it is forced upon the creature via a spell (e.g. touch of fatigue) or effect (e.g. after a barbarian's rage ends), the creature can, without fearing fatigue, perform tasks that would normally fatigue others.

• The creature can overland hustle without gaining the condition fatigued.

  A character can hustle for 1 hour without a problem. Hustling for a second hour in between sleep cycles deals 1 point of nonlethal damage, and each additional hour deals twice the damage taken during the previous hour of hustling. A character who takes any nonlethal damage from hustling becomes fatigued.

• The creature can be on a forced march without gaining the condition fatigued.

  For each hour of marching beyond 8 hours, a Constitution check (DC 10, +2 per extra hour) is required. If the check fails, the character takes 1d6 points of nonlethal damage. A character who takes any nonlethal damage from a forced march becomes fatigued.

• The creature can suffer from dehydration or starvation without gaining the condition fatigued.

  Characters who have taken nonlethal damage from lack of food or water are fatigued. Nonlethal damage from thirst or starvation cannot be recovered until the character gets food or water, as needed—not even magic that restores hit points heals this damage.

• The creature can suffer from heat exposure without gaining the condition fatigued.

  A character who takes any nonlethal damage from heat exposure now suffers from heatstroke and is fatigued. These penalties end when the character recovers from the nonlethal damage she took from the heat.

  Strangely, cold exposure usually does cause the character who is immune to fatigue to suffer as if fatigued because a creature "who takes any nonlethal damage from cold or exposure is beset by frostbite or hypothermia [and is] treat[ed...] as fatigued," instead of the creature actually being fatigued. But if the DM uses the Arctic Climate Zone's Frostbite and Hypothermia rules, creatures instead suffer for-reals fatigue. Thanks, Pathfinder!

• A creature who's swimming "must make a DC 20 Swim check or take 1d6 points of nonlethal damage from fatigue" each hour. The DM may rule that a creature who has immunity to fatigue can swim forever.
• The creature needs sleep only every other day if the rules Fatigue from Lack of Sleep are used. Others who try the same gain the condition fatigued. At the DM's discretion, as it's an effect of fatigue, the penalty to saving throws versus sleep effects is also ignored.
• The creature can traverse mountainous terrain's low peaks and high passes without risk of gaining the condition fatigued.
• The creature can rest while wearing medium or heavy armor and afterward not gain the condition fatigued.
• The creature can recklessly employ the feats Acadamae Graduate, Bolstered Resilience, Blood Vengeance, and Inner Strength without gaining the condition fatigued.
• The creature can read a dream journal of the pallid seer, hand it to other folks, then laugh as they gain the condition fatigued after they read it. Note: In addition to being an awesome magic item for the whole party, you'll make back your 600 gp in bar bets quickly ("I'll bet you 10 gp you can't read this book for an hour and not get tired! Now, sleepy-head, I bet you 20 gp I can read it for an hour and not get tired").
• The creature almost always gets the best benefit of the weapon special ability invigorating. Note: This doesn't make this weapon special ability worthwhile.
• The creature can break the DM's stories by using the 3rd-level inheritor's crusader's supernatural ability sword against injustice against everybody about anything without ever gaining the condition fatigued. Note: It's an absolute shame the prestige class inheritor's crusader is bound by the paladin's code because were it not this would be the best use of immunity to fatigue (e.g. "Did you take the cookies?" Thwack! "Did you say this armor makes me look fat?" Thwack! "Did you say I was too judgmental?" Thwack!).
• The creature can pick the either the drawback Hedonistic or the drawback Tainted Spirit and, as the creature never gains the condition fatigued, the creature never suffers the ill effects. Note: This is pretty shady and doubly so if starting a character with immunity to fatigue.

There are even more extreme corner cases (e.g. during a duel use dueling resolve without gaining the condition fatigued, ending the stalwart defender's class feature defensive stance without gaining the condition fatigued, employing the 13th-level bladebound magus's supernatural ability transfer arcana without risk of gaining the condition fatigued), but the list above is already pretty ridiculous.

Immunity to Exhaustion

Most of the time, immunity to fatigue will mean wholly unplanned immunity to exhaustion, but a handful of effects cause exhaustion directly (e.g. the spell ray of exhaustion). A character can perform the following tasks fearlessly due to immunity to exhaustion.

• The creature never needs sleep again if the rules Fatigue from Lack of Sleep are used, and the creature suffer only a -3 penalty to saving throws versus sleep effects. At the DM's discretion, as it's perhaps an effect of the condition exhausted, the penalty to saving throws versus sleep effects is also ignored. If not using these rules, there's the everwake amulet.
• The creature can use the benefit of the feat Drugged Rejuvenation more frequently and with less risk. Using it initially and every odd time thereafter gives the creature the condition sickened, but the condition sickened is replaced with the condition exhausted (I know!) every even time the benefit's employed. So the creature should just always have 2 doses.
• The creature might--although the DM is unlikely to rule that way--ignore the curse of the Blood-Slicked Mantle of The-Beast-That-Does-Not-Die. However, it's equally unlikely this 3rd-party major artifact will make an appearance in the campaign.

Obviously, the condition exhausted doesn't occur independently nearly as often as the condition fatigued.

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Magic Items
Those exploring the conditions fatigued and exhausted might be interested in either the cord of stubborn resolve or the stone of alliance or both.