# Infinite endurance

What is one factor or ability a creature needs to sustain infinite work? By work I mean physical activity, and to make it more specific running

I want a creature that can output work, or run until they literally collapse from sleep deprivation so the only thing stopping the creature from running is lack of sleep and obviously food... But eating while in motion is not the hardest thing ever. How does that creature need to evolve?

And it has to have a sleep pattern similar to that of a giraffe or whale, around 1 or 2 hours at most.

Running speed is 20 kilometers per hour, so slightly more than the average untrained human.

• You might want to look at these; en.wikipedia.org/wiki/Persistence_hunting, popularmechanics.com/adventure/sports/g418/…, pbs.org/wgbh/nova/article/… Also, some mammals are able to continue being active even while asleep (but usually swimming next to othes for cues scientificamerican.com/article/how-do-whales-and-dolphin – DWKraus May 5 at 21:35
• In case it may help, Wiki says a common swift can fly for 10 month non-stop. They drink, eat, sleep and mate on the wing. – Igor G May 5 at 22:55
• Some species of shark need to constantly swim to breath. While they don't need to "run" (a simple "walk" being as effective), you may play with the idea to provide an explanation why your creatures need to keep moving. – Adrian Colomitchi May 6 at 0:31
• You may find it interesting to read more about how ultramarathoners operate. The fellow who currently holds the 100mile record did it at 14km/h by my math: wpr.org/… My understanding is that slower runners (and longer races) end up taking naps. It's certainly standard practice to eat as you describe - small, high calorie density meals on the move. These events are common enough to have material available on them: run100s.com/ultra.htm – John Walthour May 6 at 12:59
• @IgorG There's also the Globe Skimmer Dragonfly, which are known to cross oceans. They can basically fly their whole lives and never see land - it takes multiple generations for them to complete a single ocean crossing. – Darrel Hoffman May 6 at 13:45

## Basis in Life

I want a creature that can output work, or run until they literally collapse from sleep deprivation so the only thing stopping the creature from running is lack of sleep and obviously food...

I believe the animal you are looking for, is the wolf.

Why is the Wolf a great archetype for an animal that has infinite stamina?

1. Efficiency: Wolves last for weeks without food, and are extremely efficient at digesting it:

Wolves have large stomachs and can devour 20 – 25 pounds of food at any one feeding time. However, wolves are able to survive without food for up to 2 weeks or even longer if prey is scarce. Their digestion is very efficient, with all but 5 percent of large meat feeds able to be digested.

1. Persistence: Wolves are some of the most persistent hunters on the planet, unlike most other predators, they will continue to chase down prey until they succeed.

Wolf hunts can either last minutes or hours depending on whether attacks are successful or not. If an attack fails, the wolves will continue to hunt until they are successful. It is a matter of survival.

1. Evolutionary Pressure: the wolf plays a part in the evolutionary cycle with the herbivores:

Wolves play an important role to other animal herds. Because wolves only hunt and eat sick or weak animals, they are actually helping the herds regain strength by ridding them of burden animals.

We can take these features from a wolf and enhance them, to obtain our animal with infinite stamina.

## 1: Efficiency

Wolves have large stomachs and can devour 20 – 25 pounds of food at any one feeding time. However, wolves are able to survive without food for up to 2 weeks or even longer if prey is scarce. Their digestion is very efficient, with all but 5 percent of large meat feeds able to be digested.

To maintain a good running speed, for extreme periods of time, an efficient digestive system is needed. It would have to be able to digest while running, and digest it quickly to convert it into energy.

It would also need to be able to go for long periods of time without food when needed, so that the animal could continue to chase down prey. An addition to what wolves have would probably be a pouch of some sort, for storing more food. If the animal were intelligent, it could possibly weave pouches to attach to itself to store and preserve food. If not, this pouch could be biological, like what camels have.

## 2: Persistence

Wolf hunts can either last minutes or hours depending on whether attacks are successful or not. If an attack fails, the wolves will continue to hunt until they are successful. It is a matter of survival.

Wolves can hunt for a very long time, taking as long as needed to chase down and corner prey. Their spirit of the hunt, in this regard, is extremely useful.

This, however, doesn't quite mean that they can do it forever. Eventually, they will have to stop. To make your creature persist for as long as needed, however, we can turn towards muscle memory: even in humans, unconscious/subconsciousness and muscle memory alone are capable of doing some very extreme things. For example, a wrestler was able to continue wrestling for a full 9 minutes while still being unconscious.

Your animal would have to possess an instinctive ability to run, even when their consciousness is not fully focused. They must develop their brains to a level where they can run even if they are completely unconscious.

They would also have to have a special chemical composition in their bodies. For this, we can turn towards one of the humans who possesses this trait, Dean Karnazes.

When running, you break down glucose for energy, producing lactate as a byproduct and an additional source of fuel that can also be converted back into energy. However, when you exceed your lactate threshold, your body is no longer able to convert the lactate as rapidly as it is being produced, leading to a buildup of acidity in the muscles.

But when they tested Dean, they found that his lactate threshold was almost superhuman.

Next, they performed a lactate threshold test. They said the test would take 15 minutes, tops. Finally, after an hour, they stopped the test. They said they’d never seen anything like this before.

“At a certain level of intensity, I do feel like I can go a long way without tiring,” he says. “No matter how hard I push, my muscles never seize up. That’s kind of a nice thing if I plan to run a long way... To be honest, what eventually happens is that I get sleepy. I’ve run through three nights without sleep and the third night of sleepless running was a bit psychotic. I actually experienced bouts of ‘sleep running’, where I was falling asleep while in motion, and I just willed myself to keep going.”

In this case, by combining muscle memory and an extremely high lactic acid threshold, your creature could run for as long as its willpower could hold out, until, as you said, they "run until they literally collapse from sleep deprivation".

## 3: Evolutionary Pressure

Wolves play an important role to other animal herds. Because wolves only hunt and eat sick or weak animals, they are actually helping the herds regain strength by ridding them of burden animals.

Not only are wolves highly selective in which prey they hunt down, wolves also spend a lot of time planning out an attack, usually focusing on weaker members. From this source:

A wolf pack may trail a herd of elk, caribou or other large prey for days before making its move. During this time, they are already hunting, assessing the herd, looking for an animal that displays any sign of weakness, and this is just the beginning. Wolves must also factor in other conditions that will affect the hunt; weather and terrain can tip the scales in favor of predator or prey.

This would probably be the most important requirement. For a creature that can run forever to actually evolve, it would need an opponent. Something to compete with it, and give it evolutionary pressure. By hunting down only weaker animals, the evolutionary pressure will cause both the hunter and prey to become stronger and more specialized over time.

Through countless generations, your creature will weed out the weakest of its prey, allowing the prey to feel evolutionary pressure. The prey will evolve, to have better stamina and escape the creatures. To catch them, the creatures will also experience evolutionary pressure, to catch the prey so they can continue to live. The cycle will continue, on and on.

## Conclusion

Starting with the wolf as an archetype, through many generations of natural selection, finally, the specimen that has the most efficient digestive system, mentality built for hunting down prey, a supernatural threshold towards muscle pain, and an environment and prey to showcase its infinite stamina to, will have been created.

This apex predator would persistently hunt down its prey, until the prey collapses in despair and exhaustion. Avoid the eyes of this predator, for if you catch its dreadful eyes, it will chase until the fall leaves are covered in snow, the snow melts to release spring blooms, and the spring blooms give in to summer heat. The reaper will come, strip everything clean, and look for its next prey, never resting, always running.

• I'm really interested about wolves hunting only the weaker prey, but I can't seem to find a source on how it actually works...if they selectively choose which member of an herd to attack or if they just scare the entire herd and kill whoever is slower. – user75545 May 7 at 20:26
• @Kyu I think they strategize, usually they work together to peel away the stronger members and hunt down the weaker ones. This is how a lot of predators do it too, I believe. – Enthus3d May 7 at 20:28
• @Kyu I found a resource here that describes how they plan out their hunts and target the weakest of the pack, I also included a summary and quote in my answer. Link here: livingwithwolves.org/how-wolves-hunt – Enthus3d May 7 at 20:33
• @Kyu thank you for accepting my answer, I had a lot of fun researching wolves and their hunting mechanisms. I learned a lot today, and hope the answer helps :) – Enthus3d May 7 at 20:45
• In fact, it's conceivable in this scenario that the prey would develop stamina just as high as the hunter, if not higher. – Dan May 8 at 19:59

What is one factor or ability a creature needs to sustain infinite work?

Good cooling.
Many furry animals need to stop and pant to cool themselves after hard physical activity. Your creature must be capable of dissipating heat effectively.

The first thing your species needs to conquer is sleep. Dolphins can sleep with only part of their brains, letting them remain semi-conscious 24/7. Your creature could do this too. For a few hours a day, half of its brain is asleep. It would be able to continue running during this time.

The next thing to conquer is speed. If this thing is running at 20k per hour, 24/7, it will be burning energy rapidly. 20 kph is faster than the highest trained humans can run for more than a few hours, but humans aren't optimized for running, and the fact that we can run that fast for hours shows that it's clearly possible. A quick internet search revealed that horses can run for up to 72 hours straight before they die. This creature will have to have an extremely well-made vasculature, heart, and lungs to ensure its muscles are thoroughly oxygenated.

The final obstacle to conquer is energy. This creature will be burning through energy quickly and constantly. It will probably have to eat every two or three hours and will have an extremely fast metabolism to keep energy levels high enough to continue moving. As you said, eating while running isn't that difficult as a human, so this creature will have no problem. How it gets food while moving has many possibilities.

There is no single factor that needs to be overcome for this thing to run indefinitely, but the above should cover the largest obstacles for a perpetual-running creature.

As to how it would have to evolve? It would need a selective pressure that punishes being still. Perhaps there are predators that pounce as soon as your speed drops below a threshold, or maybe it hunts herds of creatures that also continually move, so to stop is to lose your food source. There are a lot of ways you could create a selective pressure that rewards continually moving. In the ocean, there are many creatures that don't sleep as much as we do on land, probably because it's a lot more difficult to hide in the open ocean.

Hope that helps clear some things up.

• It would need a selective pressure that punishes being still. yeap, some/many species of sharks are "punished" this way – Adrian Colomitchi May 6 at 0:24
• Humans do muscular work continuously. Respiration goes on all the time, our entire lives. We can control it or it can go autonomously. There is no reason you could not have running muscles work the same way. – Willk May 6 at 0:39

Infinite endurance isn't that big a problem. After all, you already have it. You have several muscles in your body that work without pause for decades on end.

If you want your creature to run forever you need to use the same sort of muscles in the legs. However, you have some other problems:

1) As has been mentioned, heat. Humans fare very well compared to most creatures in this regard, but probably not well enough for infinite running. Your creature needs better cooling in some fashion.

2) Food. From looking at long distance hikers we can see that our digestive system maxes out at something over twice our base metabolism. You're going to have to beef up the digestive system to sustain the running.

• I think the heart would be the biggest problem for endurance. Heart failure is the main reason a horse dies after running for too long. There’s a reasons athletes have bigger hearts— they need more blood supply to their muscles. – chase leffers May 6 at 15:57
• @chaseleffers Almost all animals are sprinters, they can't maintain the pace. Humans can walk almost all of them into the ground (to the point that they can walk up to them and kill them.) – Loren Pechtel May 6 at 18:45

The most energy-efficient runners in the animal kindgom are kangaroos and wallabies. This is because of their springy legs. I found this article from Stanford University about them.

Check this excerpt (emphasis mine):

When taking a closer look at the muscular-skeletal make-up of these hind legs, one will notice unique characteristics of both the tendons and muscles. A kangaroo has extremely long tendons in its back legs that undergo drastic length changes when the kangaroo is hoping. Acting like springs, the tendons stretch under the weight of the kangaroo, and, while elongated, contain elastic energy. The muscles in a kangaroo's legs are impressively strong and stiff, allowing them to handle the stretching of the tendons. One study conducted on the animals revealed that their tendons can store up to ten times as much energy as their muscles. All of this stored energy is released when the kangaroo pushes up and the tendon contracts again. While the muscles in a kangaroos legs still work to help them hop, so much of the energy they use comes from the tendons. Unlike muscles, tendons do not fatigue and they do not require oxygen to work.

Since kangaroos garner so much of their hopping energy from the tendons in their legs, they consume oxygen at a significantly slower rate than other mammals of similar size. When studying the movement patterns of red kangaroos, one team of scientists determined that as the kangaroos increased speed over flat ground their rate of oxygen consumption stayed nearly constant. In fact, the maximum measured rate of oxygen consumption of 3.0 mL kg-1 s-1 tops all animals with exception of a few vertebrate species. A study done by the University of Wisconsin - Madison looked at oxygen consumption rate in three dogs that were trained to run on the treadmill. When looking at movement statics obtained from the two studies above, and comparing red kangaroos and dogs, it is clear kangaroos hold the advantage in efficiency statistics (...)

While the oxygen consumption rates of the two animals are similar, the Kangaroo is moving at over four times the pace of the dogs. Achieving the same oxygen consumption rate while moving at such a faster pace is truly an impressive feat for the kangaroo.

This is not a proper article, but a researcher once said this to phys.org:

"In effect, it is impossible to tire out a kangaroo while it hops over level ground."

A few more thoughts.

You said:

Running speed is 20 kilometers per hour, so slightly more than the average untrained human.

According to Wikipedia's article on fastest animals:

The comfortable hopping speed for a kangaroo is about 21–26 km/h (13–16 mph), but speeds of up to 71 km/h (44 mph) can be attained over short distances, while it can sustain a speed of 40 km/h (25 mph) for nearly 2 km (1.2 mi). The faster a kangaroo hops, the less energy it consumes (up to its cruising speed).

Also this:

And it has to have a sleep pattern similar to that of a giraffe or whale, around 1 or 2 hours at most.

Some googling suggests that in the wild, Kangaroos spend 2 to 4 hours in deep sleep per day. As prey animals they must always be wary of predators, so most of the time they don't spend grazing (or mating, fighting etc.) they just rest lightly.

Food requirements
Putting some numbers to the calorie requirement for human equivalent:

• Human running: ~1000-1500 Cal/hr
• Fat ~9 cal/g; protein/sugar ~4cal/g
• Food requirement ~200-250g/hr -> 5-6 kg/day
• That much weight is probably going to slow them down by about ~10s/km* => ~19km/hr which is not an insiginficant speed drop.
• Can they stash + grab food? (see ultramarathon aid stations)

*Source: https://runbundle.com/tools/weight-vs-pace-calculator Start weight = 75kg, distance=5km, pace = 3min/km

Digesting
This actually takes a lot of energy/time, if your bloodflow is going to muscles then you will likely struggle to digest food efficiently.

Oxygen Any distance running is going to require buckets loads of oxygen as anaerobic respiration isn't sustainable for humans (If you can make this work then you might solve some other problems too!), so big lungs (which aren't compressed while in running position) with a strong diaphragm are a must.

Sleeping and Cooling are important too and dealt with in other answers

Running speed is 20 kilometers per hour, so slightly more than the average untrained human.

That's a lot more than an untrained human! That pace would be enough to earn you an Olympic starting place for Womens 5km or Mens Marathon.