This character is an elf-human hybrid, who can travel long distances at high speeds with little rest. She can run at top speed (what we call sprinting) without stopping to rest, sleep or eat for three days. It is generally accepted that elves are very hardy and fast, case in point: Legolas from Lord of the Rings or Arya from the Inheritance cycle.

My question: How would an elf or an elf-human hybrid gain the energy he/she needs to run such long distances, at such high speeds, without rest, sleep, or food? The energy needed must come from somewhere, but the concept of an elf needing to gorge on mountains of food to keep up his strength seems a bit vulgar. On the other hand, elves don't have slow metabolisms: I've never heard of a fat elf...

  • 1
    $\begingroup$ One aspect of your question is actually known from human biology - there's a man that can apparently keep running without his muscles becoming tired: theguardian.com/lifeandstyle/the-running-blog/2013/aug/30/… (he still needs to sleep eventually) $\endgroup$
    – Peter S.
    Apr 7, 2016 at 15:02
  • $\begingroup$ Are you looking for reasonably science based answers or just a general explanation? $\endgroup$
    – bowlturner
    Apr 7, 2016 at 15:03
  • $\begingroup$ @bowlturner, Just something that would make sense, I guess? Because the energy definitely has to come from somewhere? Magic-related answers would certainly be great too! $\endgroup$
    – ASH-Aisyah
    Apr 7, 2016 at 15:09
  • $\begingroup$ @PeterS. Whoa! I see, so a lot of enzymes and mitochondria would make it possible! Thanks! $\endgroup$
    – ASH-Aisyah
    Apr 7, 2016 at 15:12
  • $\begingroup$ @PeterS. That is crazy. But I would hazard a guess that stressing the body like that has the potential to wear on the human body rather significantly. $\endgroup$
    – James
    Apr 7, 2016 at 15:45

8 Answers 8


So, elves are creatures that are rather heavy on magic, so this sort of feat is not a big deal if you just answer - "hey, it's magic!" But that is a cheap answer... unless you stop to realize that what you are asking really goes to the question: how can magic happen and still follow conservation of energy?

Basically, we humans store the energy we get from food in these molecules called Adenosine Triphosphate (ATP). But any being that would be able to perform feats like this would have to use a different way of storing and freeing up energy - a different molecule that could store up a lot more energy, and a lot more of it.

According to Wikipedia, we only have about 250 grams of ATP in our body, but turn over the equivalent of our entire weight, worth of ATP, in one day. That seems hard to believe, but gives a good gist. Imagine a being that has as much as a kilo of Adeno-TriHeptose-Pentaphosphate, and can turn over five times her body weight of it in a day. ATP is adenine with two molecules of C5H10O5 and three phosphates. This molecule i am making up, ATHPP (probably cannot exist) is Adenine with three molecules of a much more complex sugar (C7H14O7) and five phosphates. This being is basically a walking gas can - no smoking in her vicinity, please.

By the way, adenine is used to control heart rythm, if I remember correctly, so the additional adenine would help explain why his heart-rate does not go through the roof when he uses that much energy. Also, the vast storage of sugar also explains why they are not much affected by alcoholic drinks.

You don't need lots of food, you mostly need highly concentrated sugars. Equip this gal with a pack filled with momma's special recipe syrup, and let her rip.

  • $\begingroup$ Would it work, though? I'm not a biologist, but ATP seems for me to be a method of energy transmission, not storage ("we only have about 250 grams of ATP in our body, but turn over the equivalent of our entire weight, worth of ATP, in one day"). I mean, there is not much surplus ATP just lying around as energy reserve, like fat, so you would need to increase energy production first rather than improving ATP. But to get more energy you need not only enough food (where sugar would help, as you suggested), but also more oxygen - thus imho the main bottleneck are lungs and hemoglobin efficiency $\endgroup$
    – Ijon
    Sep 1, 2019 at 10:26
  • $\begingroup$ @ljon - I have no idea. I am not a biologist either. If it is even true that we recycle our body weight in ATP, in one day, there would have to be some major recycling going on. And yes, oxygen intake would be an issue, but easily resolved by hand-waving in a supremely more efficient set of lungs with a far better gas exchange mechanism. Same goes for hemoglobin. It's a given this being's biology is vastly different from ours. $\endgroup$
    – user11864
    Sep 3, 2019 at 19:54


Brute-force is not very Elfish, so i'll go with a more clever and nimble solution: Energy efficiency.

  • Part 1: Staying alive

If our elf uses as many calories per km as a human sprinting, she will overheat and die very quickly.

If she has speed and caloric mileage comparable to a human marathon runner, she will face the same thermal challenges, which means she'll have to wear very light clothes, leave the mithril mail at home, and require frequent hydration, including salts and electrolytes. This is independent of her endurance, stamina, etc. The volume of water a person can sweat before dropping isn't that much.

So, higher metabolic rate isn't the answer. Also, as explained by James, higher power output creates more waste the body has to get rid of.

She will need to do it with less energy that a human, which boils down to: how to make running more efficient?

  • Part 2: Biomechanics

When we humans run, most of the energy is consumed in raising the center of mass of the body once per step, and this energy is not recovered when the center of mass is lowered again. Very little energy is expended towards overcoming air friction.

This is why someone in decent shape can ride a bicycle at 20km/h with less than 100 heart rate. This is a barely noticeable effort which can be sustained almost all day. Can't be compared AT ALL to running at the same speed...

Running at 20km/h should require 2-300 watts of mechanical power, which due to our efficiency of around 25% translates to about 800-1200W input chemical power (ie, food)... and output thermal power (ie, heating).

Now, let's draw inspiration from an amazing animal:

As red kangaroos hop faster over level ground, their rate of oxygen consumption (indicating metabolic energy consumption) remains nearly the same. This phenomenon has been attributed to exceptional elastic energy storage and recovery via long compliant tendons in the legs.


So, kangaroo have KERS (Kinetic Energy Recovery Systems) like F1 cars.

Let's equip our Elves with a few elastic tendons in their legs. Now, picture an elf running. When the front foot touches down, the knee and ankle joints flex, and the springy tendons store energy, which is then recovered to propel the elf forward on the next stride. Just like kangaroos.

Springy tendons also reduce the strain on joints and muscles, which is important for long distances.

Plus, this should give our elf a nimble, agile and quiet gait, which is very in-character.

Since Elves make the best swords and the best gear, they also make the best shoes, so she'll have blister-proof Fantasy Air sneakers.

Let's also give her an elvin agility bonus, and fudge this to 50% energy savings.

We're down to 100-150 watts, which is still a bit less efficient than a mountain bike with big knobbly tires, but a lot better than before.

Now, we give another elvin bonuses:

  • Increase metabolic efficiency to 35% instead of the human 25%
  • Optimize metabolism to burn fat more efficiently than humans.

She still produces 100-150 watts mechanical. However, increased efficiency means she needs to burn less calories to do so, therefore sweating a lot less, and needing less water. She doesn't need unrealistic lungs or heart either. She will also burn mostly fat. So, she needs 40 grams of fat per hour, or 30 grams fat plus 20 grams sugar. Pastries (ie, Lembas) should be fine.

Reducing (not increasing) her metabolic needs seems to be the way to go.

Fat will carry her much further without eating, as body fat reserves are quite important (even for someone who looks like a stick figure) whereas sugar reserves are not.

Now, some of that energy could also come from a magical source, of course. Or her magic could help with the pesky logistic details, like joint pains, blisters, etc.

Just don't make her run for a week in plate armor.


Elves are more efficient, thus use less power, and as a result Legolas arrives at the end of the trip with fabulous hair, looking relaxed, and without breaking a sweat.

Meanwhile, the dwarf sweats gallons in his heavy armor, stinks, and blames it all on the elf.

  • $\begingroup$ Hello and welcome to WorldBuilding.SE! Excellent first answer. The paragraph that starts with a bold "Reducing" doesn't have an end. Would you mind editing your answer to finish that one? All in all: that's the way to go. If you got questions please take the tour and visit the help center. Have fun! $\endgroup$
    – Secespitus
    Mar 14, 2017 at 21:44

Since you already referred to Legolas, I would say your Elves found the recipe to make lembas.
A special type of biscuit that is extremely nourishing and can sustain a Elf or Human for an entire day.

Some care must be taken though as Merry and Pippin found out. If you combine it with Entish drinks some strange things may happen...

Seems your runner will be fine if she just eats a bit more if this stuff than is normal.

  • $\begingroup$ Yeahp, I did think of lembas! Actually, that would be a great solution, if only we knew what is in it... :) $\endgroup$
    – ASH-Aisyah
    Apr 7, 2016 at 15:38
  • 5
    $\begingroup$ @ASH-Aisyah It's probably a mixture of Unobtainium, Handwavium and an equal part of Belief. Of course, it tastes best when you take it with a grain of salt. $\endgroup$
    – Tonny
    Apr 7, 2016 at 15:44
  • 1
    $\begingroup$ @ASH-Aisyah Don't forget Magicium $\endgroup$ Apr 8, 2016 at 13:46
  • $\begingroup$ It could be made out of some kind of high energy density fossil fuel like diesel! Fossil fuels are organic and it is theoretically possible for a living organism to metabolize them...we can't because we didn't evolve in a world where diesel-fruits grow on trees, but maybe elves did. Of course, this does mean that non-elves will be unable to eat elf-bread. $\endgroup$ Feb 12, 2019 at 12:26

Well, first I would say that Elves would need to have an incredibly efficient metabolism, Allowing them to use less energy to perform similar tasks to others.

On top of that part of the efficiency is magic based. It works at a subconscious level. And the elves tend to regenerate this magic store when around areas that resonate with their nature. Tree elves rejuvenate in forests etc. They could also perform rituals to help speed up the process or to work in place of a physical setting.

But the magic helps fuel the body, keep fatigue away and repairs minor damage from the exertion. Well fed elves will use less magic to perform the same tasks, and eventually an elf will hit it's limits if it can't fill up it's reserves.

  • $\begingroup$ 'elves tend to regenerate this magic store when around areas that resonate with their nature'. Very interesting, I didn't think of that. Thank you! This was great! $\endgroup$
    – ASH-Aisyah
    Apr 7, 2016 at 15:39

Welcome to the site ASH,

I think you are probably stuck with a magically enhanced energy creation, storage and usage system...not to mention clean up.

The system humans have in place it incredible elaborate. We have systems specifically designed to provide nutrients and oxygen while simultaneously removing cellular waste and we are nowhere near efficient enough to run at a sprint for three straight days.


  • Caloric intake versus burn.

A marathon runner, who is not spriting, will burn roughly 100 calories per mile during a race, which roughs out to 2600 calories for a full marathon and on average a marathon is run in around 4 hours and 20 minutes.

This puts your elf/hybrid caloric burn at something like, 46,800 calories for your three day jaunt. To manage that you would have to eat 86.32 big macs.

Keep in mind, this is not at sprinting speed...this is marathon pace

  • Waste removal.

When your body burns its fuel it creates waste, when it burns a lot of fuel quickly it creates more waste than it can process and goes into oxygen debt. There is simply no way a human, or purely biological system could handle moving that much for that long.

Those are the two biggest, most directly related problems, but there are others as well.

The cushioning systems between bones and the strength of the bones themselves would have to be improved. Lungs would need to be larger, and the heart bigger. Exhaustion has impacts on coordination and balance not to mention its impacts on cognitive function.

Oh right and muscle fibers would have to be vastly improved...stronger, more flexible, etc etc etc.

In short, the answer to your question is a magically enhanced metabolism.

...but in short is boring. :)

  • $\begingroup$ Thank you James! This site was a great discovery :)! What is our opinion on PeterS.'s contribution in the comments' section? $\endgroup$
    – ASH-Aisyah
    Apr 7, 2016 at 15:36
  • 1
    $\begingroup$ @ASH-Aisyah That is a crazy article. But I would assume you want there to be no side effects to your 3 day jaunt and that this is "normal" for your elves. So that crazy dude aside...also note that cells have only so much real estate, and while more mitochondria can make you more efficient you still have to get the raw materials to the cells. Same with enzymes... $\endgroup$
    – James
    Apr 7, 2016 at 15:48
  • $\begingroup$ I have a friend who runs ultra-marathons - 100k. He says the part he hates the most is that his toenails start to split after the first 50 miles. By the end, his feet are a mess and it takes weeks to recover. $\endgroup$
    – user11864
    Apr 7, 2016 at 17:08

This is actually not that surprising of a feat. Tolkien's elves are exceptionally lightweight (magic) and humans are one of the best endurance animals in existence, so combine the two and the feets makes sense.

Elves are described and shown to be exceptionally light weight (one book describes them as walking on top of soft snow without sinking) magic is the only given answer as to why they are so light, but that alone would make for some very big feats of endurance since they are moving less mass around.

Real world humans have exceptional endurance, remember the tour de france used to be a 6 day foot race and Dean Karnazes ran for 3 and half days without stopping. Normal fit humans can walk a horse to death and as shown trained humans run for days without stopping, sleep forces them to stop before anything else. Part of this is becasue humans are built for endurance but part of it is also that human have exceptional willpower.

now combine exceptional endurance with a body so lightweight sprinting is not any harder than walking and your described feats seem quite reasonable.


There isn't really a magical way to gain more energy. Not without using magic, anyway. Instead you just use the energy more efficiently. Humans are already more efficient long distance runners than most animals, so I'll just pick on some specific points.

Aerobic metabolism.

Better lungs, better blood circulation, more haemoglobin, more mitochondria, better sugar storage, and changes to metabolism and enzymes to support the above. Most of this would simply be human+ and fairly self-explanatory. And irrelevant unless the character gets captured by a mad scientist.

But lungs is something there you could do a significant improvement and get a significant boost. The best model to copy would probably be bird lungs.

Reduced weight

Less weight to carry, less energy wasted. Elves are usually described having slender builds anyway, so that is a no-brainer. If you use the avian lungs option, you can also copy the hollow bones. And should as they link with the respiratory system. This is naturally pointless if you then strap on massive armor, but elves should weight less than humans.

Heat management

Excess heat and getting rid of it is a major source of long term inefficiency for humans. I'd suggest using the improved lungs to get rid of more heat and sweating less. Another easy (not really, but it is easy to write) adaptations is to make elves tolerate variable body temperature. 36°C/97 F when standing still, up to 39°C/102F when exerting themselves. This should improve efficiency in both modes. You could make the variability smaller for the head by adding extra blood flow control on the neck. You could also make the hair double as heat radiator to help cool the head while running and justify some exotic hair colors. (The hair would have better heat conduction and the scalp would have a "thermostat" to control heat transfer to the hair.)


A tall order, this 3 day sprint with no rest. She is going to have to drink and she is going to need salt. Here are my ideas about the rest.

  1. Long distance running. There is nothing better than humans at long distance running. Animals beat us for strength and speed but a human can run down just about anything given time.


We will say her human dad was a champion distance runner with all the oxygen deliver, slow twitch muscle etc that entails.

  1. Liger principle. Your hero is a hybrid. Sometimes in a hybrid, genes which mask or reduce effect of a gene are not transmitted meaning the gene is unsuppressed in the hybrid. In lions, contributions from the male increase size and from the female limit size. If the mom is a tiger there is no size limit contribution. The result: ligers are huge. http://blogs.discovermagazine.com/gnxp/2009/09/why-ligers-are-huge/#.WMiNABiZMk8

Humans are weaker than other apes because of some issue with our muscle - it does not activate as thoroughly or completely as is the case for chimps. The linked article suggests that this contributes to fine motor control; ok. Another theory is that loads of brute force at the ready increases the chance of killing a baby by accident and weakening humans makes babies safer. Just as the tiger is genetically distant enough from the lion that growth enhancing genes are not masked, the elf is distant enough from the human that genes allowing maximal muscle use are not masked. The sacrifice is that you lose the fine tuned muscle activation that lets humans do delicate tasks. So she is a little awkward. But freaking burly!

  1. Elves run higher hemoglobin levels. Why? Elves have diverged less from the aquatic common ancestor of elves and humans and are adapted for breath holding. Elves notwithstanding, the idea that humans were aquatic apes is a cool one. https://www.amazon.com/Scars-Evolution-bodies-about-origins-ebook/dp/B00844ORDK

Higher hemoglobin means better blood delivery, especially in sprintlike conditions. It will take more for her muscles to go anaerobic. That is why athletes do blood doping. Her hemoglobin of 19 means she is not going to be vanilla fair, if she is white-skinned. More the ruddy glow of health (and lots of blood).

  1. Her sprint is not really that fast and so she does not really get to anaerobic (which is unsustainable for 3 days). Partly because of the burly. Also because of #5.

  2. She is fat. In all the right places and the other places too. She was never a skinny girl, but the current degree of fatness is your fault, ASH-Aisyah and she is not pleased with you. But if she has to be able to run 3 full days without eating that fuel has got to be on board somewhere. To clarify she is not a bouncy Venus of Willendorf fat but fat like a seal; fat everywhere. See #3. Your half-elf is an even better swimmer than she is a runner.

  3. She is drunk. You prohibited eating but not drinking. Humans need more water that most because our perspiration, wasteful when we are not moving fast, is key to keeping cool during prolonged exercise. You need something to sweat out. Additionally, sweat costs salt, which is why distance runners should not drink pure water but water with electrolyte. But she is drunk because her drink is a salted 40 proof spirit, invented for exactly this purpose. The ethanol is excellent fuel, comparable to fat in energy density and will not cause her to break the ketogenic state she needs to burn her fat for energy.

  4. She is naked. Your hero is proud of her own skin, and clothes are wasted weight. Plus extra surface area for sweat helps the cooling.

  5. She smells terrific. That salted spirit is flavored with special herbs that come right out thru the pores, like cinnamon schnapps or garlic. But these elf herbs smell more like green Chartreuse crossed with Old Spice.

  6. She is high. Those herbs work like coca leaves, which is how she can do the 3 days without sleep.

Your ruddy, muscular, clumsy, overweight, naked, drunk, high, great smelling elf/human hybrid. Oh yeah! She will run you into the ground.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .