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Previous parts here:

Creating a scientificly semi-valid super-soldier, part 1: Skeleton
Creating a scientificly semi-valid super-soldier, part 2: nervous system
Creating a scientificly semi-valid super-soldier, part 3: Physical shock resistance

After running a mile or fighting through fifty bad guys it's a rare sight to see a hero or villain be panting exhaustedly. In fact, the more capable and genetically altered they are the less oxygen they seem to need instead of more.

So how could you design a (preferably humanoid) creature with improved lungs? The main focus of the question lies on getting as much oxygen volume into your blood as possible per unit of time, but things like lung tissue capable of withstanding violent shocks without rupturing are welcome idea's as well.

Keep in mind: In our current lungs there's no "wind" in the respiratory lobules. The passage of air into them happens purely on diffusion. Additionally, we don't want lungs that will cause our super-creature to be easily susceptible to dust, viruses, bacteria and fungi that are in the air and can clog up or infect the lungs.

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  • $\begingroup$ I've no idea how you'd go about it so I won't pop it in as an answer but have you considered an oxygen storage organ, some way it extracts & stores oxygen from the atmosphere with the store organ triggered by the adrenal system to flood it's lungs with pure 100% oxygen when the adrenalin kicks in? $\endgroup$ – Pelinore Apr 4 '18 at 10:23
  • $\begingroup$ Also, does the effect have to be a natural function of it's own body or even from an organic source, would a tech implant of some sort qualify? $\endgroup$ – Pelinore Apr 4 '18 at 10:29
  • $\begingroup$ Why not just make them more effective at using anaerobic respiration - Its something Humans already can do, but limited. $\endgroup$ – Daniel Apr 4 '18 at 11:55
  • $\begingroup$ @Daniel Because anaerobic respiration is much less energy efficient than aerobic respiration. $\endgroup$ – Jack Aidley Apr 4 '18 at 13:37
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    $\begingroup$ @Jack Aidley: After running a mile or fighting through fifty bad guys - without panting exhaustedly at the end was the goal I had in mind - sure not eliminating Oxygen usage completely. So I guess we can agree this could be some solution for the super soldier? $\endgroup$ – Daniel Apr 5 '18 at 23:03
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I've already asked two question in this site that maybe could help you in order to make your super soldier, also, I'll explain them and try to produce more ideas:

  1. How to increase the efficiency of lungs;
  2. How to make a human that doesn't need breath;

Bird respiratory system

P.S: if you or someone decide to give me an upvote for this, instead give that to JDługosz♦. enter image description here From Wikipedia:

The cross-current respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from right to left in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram). Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.

This respiratory system let birds to simulate and inhale and exhale at the same time, "basically doubling" (don't exactly) the amount of air absorbed. They have air sacs: while they inhale, the 50% of air goes to some air sacs with O2, and the another 50% is consumed and stored as CO2 in another sacs, during exhalation, the 50% of O2 in air sacs is consumed and expelled, while at the same time the 50% of C02 in air sacs is just exhaled (they are able to get oxygen even when they are exhaling, thing that we can't do).

  • If you don't understand how it works, read the wikipedia's link, in this diagram wasn't show but birds also have air sacs to store air. If you keep without understanding, ask me in comments and I will try to help you. It took me a while to also understand it :).
  • This system is more vulnerable to CO2 inhalation (breath faster the toxic -> die faster), also is more vulnerable to hold breath.
    • Maybe they may have a hybrid mammal and bird respiratory system. Like a smaller lung, or adapted air sacs in order to also be able to absorb the storaged oxygen.

Hemogoblin, myoglobin and (2,3-BPG)

P.S: if you or someone decide to give me an upvote for this, instead you should consider give it to Aaron Barnard, P Chapman and/or elemtilas.

Futhemorer do anatomical changes we can also do some microscopic but not less important adaptations.

Hemogoblin:

I am quite sure you have heard at least one time in school about this protein, it transports oxygen from the lungs to the body cells, and also transport the carbon dioxide from the body cells to the lung. Actually, people who live in high altitudes (like mountains with low oxygen) or people who smoke have an increase of this compound in their blood (red blood cells), as a response from the body to a decrease of oxygen intake: the body increase the absorbtion efficiency. You soldiers could have a higher concetration on this in blood.

Myoglobin:

High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin. Myoglobin is found in Type I muscle, Type II A and Type II B, but most texts consider myoglobin not to be found in smooth muscle.

2,3-Bisphosphoglyceric acid:

2,3-BPG is present in human red blood cells (RBC; erythrocyte) at approximately 5 mmol/L. It binds with greater affinity to deoxygenated hemoglobin (e.g. when the red blood cell is near respiring tissue) than it does to oxygenated hemoglobin (e.g., in the lungs) due to spatial changes: 2,3-BPG (with an estimated size of about 9 angstroms) fits in the deoxygenated hemoglobin configuration (11 angstroms), but not as well in the oxygenated (5 angstroms). It interacts with deoxygenated hemoglobin beta subunits by decreasing their affinity for oxygen, so it allosterically promotes the release of the remaining oxygen molecules bound to the hemoglobin, thus enhancing the ability of RBCs to release oxygen near tissues that need it most. 2,3-BPG is thus an allosteric effector.

Emphasis mine of both quotes. Quotes from Wikipedia. Great! Right? Well, it's quite difficult to understand, it took me around a while to understand well how it works exactly when Aaron Barnard posts it.

In other words, 2-3BPG has an affinity to red blood cell with a low amount of oxygen in their hemoglobin because they are near muscles and are releasing it. When this chemical combine with hemoglobin it decreases the affinity (ability to retain) oxygen, releasing it even faster to the muscles; oxygenating tissues and being able quicker to travel to lungs in order to re-oxygenate.

Actually, people who live in higher places have an increase in this chemical. 2,3-BPG helps the body to resist hypoxia and other oxygen privation situation or diseases. Also, remember that create 2,3-BPG consume energy (which can be used in muscles):

There is a delicate balance between the need to generate ATP to support energy requirements for cell metabolism and the need to maintain appropriate oxygenation/deoxygenation status of hemoglobin. This balance is maintained by isomerisation of 1,3-BPG to 2,3-BPG, which enhances the deoxygenation of hemoglobin. Low pH activates the activity of biphosphoglyceromutase and inhibits bisphosphoglyerate phosphatase, which leads to increases in 2,3-BPG.

enter image description here

And:

Like hemoglobin, myoglobin is a cytoplasmic protein that binds oxygen on a heme group. It harbors only one heme group, whereas hemoglobin has four. Although its heme group is identical to those in Hb, Mb has a higher affinity for oxygen than does hemoglobin. This difference is related to its different role: whereas hemoglobin transports oxygen, myoglobin's function is to store oxygen [generally in muscles].

Emphasis (bold and itallic) and square brackets mine. Quotes from Wikipedia.

Better Spleen

I have read somewhere [citation needed :(, I think wikipedia] that exist some drugs that gives us the innate ability of some mammals: increase amount of blood cells during excercise activities (the spleen in some animals -very little in humans- has the ability to store red blood cells and produce them [we lose that ability after born]) but in humans it could produce heart problems because our heat can't beat with a denser blood, we need an stronger one.

Myocyte (AKA: muscle cells)

An introduction from Wikipedia:

A myocyte (also known as a muscle cell) is the type of cell found in muscle tissue. Myocytes are long, tubular cells that develop from myoblasts to form muscles in a process known as myogenesis. There are various specialized forms of myocytes: cardiac, skeletal, and smooth muscle cells, with various properties. The striated cells of cardiac and skeletal muscles are referred to as muscle fibers.3 Cardiomyocytes are the muscle fibres that form the chambers of the heart, and have a single central nucleus.4 Skeletal muscle fibers help support and move the body and tend to have peripheral nuclei.[5][6] Smooth muscle cells control involuntary movements such as the peristalsis contractions in the oesophagus and stomach.

In this link you will find a bit below a large table that explains the difference between 3 types of muscle cells. Each type of muscle cell has different characteristics, I am not a medic but after reading a bit I get to the conclusion that:

  • Type I fibers (Slow Oxidative (SO)) are basically "slow" muscles... they consume less oxygen and can work without getting tired a lot more time, but they are weaker and slower.
  • Type IIA fibers (Fast Oxidative/Glycolytic (FOG)) are "intermediate/fast" muscles: they consume more oxygen, are faster, a bit more stronger and can resist quite well fatigue, but not for an unlimited time (they have fewer capillaries density so I guess they resupply oxygen slower, but they store some energy inside).
  • Type IIX fibers (Fast Glycolytic (FG)) are "fast and strong" muscle cells: they are fast and the strongest ones, but they lack of fatigue resistance and store a lot less oxygen and energy inside them.

Don't worry! You don't have to choose only one type of fiber! Muscles are made by a composition of X% type I, Y% type IIA and Z% of IIX, so you could archive the best combination of durability and force/speed for each muscle in their bodies!

Also, I think that people which trains doing exercise can increase the amount slow-tissue-slow-oxygen-consumption up to 90%. In this link about the Narwhal there is a comparison with Narwhal muscles and marathon people.

Blood circulation on tissues regulation

The Narwhal is a marine animal able to dive really deep (record of 1.864 metres below water) during a decent amount of time (30 minutes normally, and up to 3 hours during winter).
They are able to do this thanks to this characteristics:

  • They have a high amount of myoglobin in their muscles. (Talked above about it).
  • During hypoxia situation it's able to priorize the blood flow only to vital organs as brain, lungs and kidneys, reducing it oxygen consumption (non-vital organs reduce their consumption) and priorizing it to better places.
  • Oposite as Dolphins, they don't have "fast-muscles", instead they use slow contraction muscles (also know as "red muscle") (87% instead of 40-50%). (Talked above about it). This kind of muscle consume less oxygen and is highly ressistent fatigue.

Lactic acid fermentation

I found a better explanation in the Spanish link of Wikipedia so I'll try to do my best to translate it:

Lactic fermentation is done on muscular tissue when there is an intense anaerobic exercise, in other words, there isn't enough oxygen supply to muscles in order to perform aerobic respiration.
When lactic acid is acumulated on muscular cells it produce symptoms of muscular fatigue. Some cells, like eritrocites (red blood cells) hasn't mitochondrias so they are forced to get energy using lactic fermentation. On the contrary, the parenchyma die quickly because it doesn't do fermentation, and it only energy source is aerobic respiration.

In other words, when there isn't enough oxygen in your body, your muscular cells switch to an anaerobic respiration: lactic fermentation. The problem is that the lactic acid... is acid, and your body doesn't like acid (acidosis). So your cells try to expulse that acid and send it to the bloodstream, the problem is that our cells aren't able to expulse it with enough fast, and it acumulate inside them, producing pain. Your super soldiers could have better bodies modified to be able to use it more frequently without problems.

I won't explain the citric acid cycle nor this one (because I am not a biologist and they are too large), but I'll try to give basic explanation to you:

  • Glycolysis: 1 Glucose + 2 ATP + 2 ADP + 2 P + 2 NAD+2 pyruvate + 4 ATP + 2 NADH + 2H+ + 2 H2O
  • 1 Pyruvate + 1 NAD+ + CoA → 1 Acetyl-CoA + NADH + CO2 + H+
    • Citric Acid Cycle: 1 Acetil-CoA + 3 NAD+ + FAD + GDP + Pi + 2 H2O → CoA-SH + 3 (NADH + H+) + FADH2 + GTP + 2 CO2
      • Several more steps (8?) with GTP and NADH (also with FADH2?) → TOTAL NET29.85 ATP to 30 ATP, with a theorical max of 36 ATP. (Biology isn't exactly, it's random).
  • Lactic acid fermentation 1 Pyruvate + NADH → Lactic acid + NAD+ + 2 ATP

    • So 2 ATP from Glycolysis + 2 ATP from Lactic fermentation → 4 ATP instead of around 29.85 - 30 ATP. Obviously Krebs Cycle (citric acid cycle) is better, but it needs oxygen, that is why our body only use it on emergency (low O2), your soldiers will need to eat more calories due to the low efficiency of fermentation.

    Looks this cute lactic acid fermentation animation: enter image description here

Edit: @Demigan pointed in comments:

  • FYI, lactic acid does not damage the cells. It has long been thought so as whenever lactic acid was present so did muscle pains, but tests showed that your cells suffer no ill effects from the lactic acid, it just happens to coincide with the work you did and because of that the amount of pain you might experience. Unfortunately, it's rather hard changing something relatively minor that is being used in textbooks and sports everywhere.

So I have read a bit more and I found also something similar, I put a quote because I didn't understand it enough in order to take my own conclusions:

  • In 2004 Robergs et al. maintained that lactic acidosis during exercise is a "construct" or myth, pointing out that part of the H+ comes from ATP hydrolysis (ATP4- + H2O → ADP3- + HPO2-4 + H+), and that reducing pyruvate to lactate (pyruvate- + NADH + H+ → lactate- + NAD+) actually consumes H+. Lindinger et al. countered that they had ignored the causative factors of the increase in [H+]. After all, the production of lactate- from a neutral molecule must increase [H+] to maintain electroneutrality. The point of Robergs's paper, however, was that lactate- is produced from pyruvate-, which has the same charge. It is pyruvate- production from neutral glucose that generates H+:

    • Glucose + 2 NAD+ + 2 ADP3- + 2 HPO2-4 → 2 pyruvate- + 2 H+ + 2 NADH + 2 ATP4- + 2 H2O

    Subsequent lactate− production absorbs these protons:

    • 2 pyruvate- + 2 H+ + 2 NADH → 2 lactate ion- + 2 NAD+

    Overall:

    • Glucose + 2 NAD+ + 2 ADP3- + 2 HPO2−4 → 2 pyruvate- + 2 H+ + 2 NADH + 2 ATP4− + 2 H2O → 2 lactic ion + 2 NAD+ + 2 ATP4− + 2 H2O

    Although the reaction glucose → 2 lactate- + 2 H+ releases two H+ when viewed on its own, the H+ are absorbed in the production of ATP. On the other hand, the absorbed acidity is released during subsequent hydrolysis of ATP: ATP4− + H2O → ADP3− + HPO2−4 + H+. So once the use of the ATP is included, the overall reaction is:

    • Glucose → 2 pyruvate- + 2 H+

    The generation of CO2 during respiration also causes an increase in [H+].

    Quote from Wikipedia. I've replaced some complex chemical formulas to its chemical names.

Cori cycle

Did you still remember all that I've said about the lactic acid fermentation, this is why I was talking about it:

The Cori cycle (also known as the Lactic acid cycle) [...] refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is metabolized back to lactate.

Our muscles cells are too focused on "being" muscles and so they aren't able to get energy efficiently and quickly, so they centralized part of this task to the liver.

Basically our muscles consumes glucose and produces lactic acid, which is send to the liver and is returned into glucose (with a slightly net energy loss) in order to be re-sent to muscles again.

enter image description here

If you don't understand this picture you can go to the Spanish Wikipedia, they have a more colorful version of it :) (If you want I can edit it with pain).

Muscular activity requires ATP, which is provided by the breakdown of glycogen in the skeletal muscles. The breakdown of glycogen, a process is known as glycogenolysis, releases glucose in the form of glucose-1-phosphate (G-1-P). The G-1-P is converted to G-6-P by the enzyme phosphoglucomutase. G-6-P is readily fed into glycolysis, [...] a process that provides ATP to the muscle cells as an energy source. During a muscular activity, the store of ATP needs to be constantly replenished. When the supply of oxygen is sufficient, this energy comes from feeding pyruvate, one product of glycolysis, into the Krebs cycle.

Emphasis and adaptation mine.

But, what happens if you don't have enough oxygen? Muscles consumes around 7 to 40 times more glucogen and oxygen during activity [spanish Wikipedia]. Obviously, the lactic acid fermentation which produces a lesser amount of energy without oxygen (Also regenerate NAD+ making easier the glycolysis). Thatis the first part of the Cori cycle.

Instead of accumulating inside the muscle cells, lactate produced by anaerobic fermentation is taken up by the liver (using the delivered by the bloodstream). This initiates the other half of the Cori cycle. In the liver, gluconeogenesis occurs. From an intuitive perspective, gluconeogenesis reverses both glycolysis and fermentation by converting lactate first into pyruvate, and finally back to glucose. The glucose is then supplied to the muscles through the bloodstream; it is ready to be fed into further glycolysis reactions. If muscle activity has stopped, the glucose is used to replenish the supplies of glycogen through glycogenesis.

Remember that as I said before, this is an inefficient cycle, but at least it helps the muscles:

Overall, the glycolysis part of the cycle produces 2 ATP molecules at a cost of 6 ATP molecules consumed in the gluconeogenesis part. Each iteration of the cycle must be maintained by a net consumption of 4 ATP molecules. As a result, the cycle cannot be sustained indefinitely. The intensive consumption of ATP molecules indicates that the Cori cycle shifts the metabolic burden from the muscles to the liver.

  • Glucose + 2ADP → 2 lactic acid + 2H+ + 2ATP + 2H20 (muscle)
  • 2 lactic acid + 6 ATP + 4 H20 --> glucose + 6ADP (liver)
  • Net energy loss: 4 ATP

Luckily, if you finish your activity, this cycle becomes more efficient:

The cycle is also important in producing ATP, an energy source, during muscle activity. The Cori cycle functions more efficiently when muscle activity has ceased. This allows the oxygen debt to be repaid such that the Krebs cycle and electron transport chain can produce energy at peak efficiency

The Spanish wikipedia said that you can get painfully tired of doing exercise because our liver isn't enough fast to do all these reactions, so some of the lactic acids get involuntary stored in muscular cells producing acidosis. Maybe having a bigger liver (or several small in strategic locations) can help our mucles. Or maybe increasing the activity of the adrenal gland to produce more adrenaline hormone which activates the Cori cycle in the liver (Futhemorer to glucagon).

Additional information

Futhemorer the Cory Cycle there is very other similar cycle called Cahill, it isn't used when the body is doing activity, it's used when you are starving, so muscles start feeding with amino-acids to keep working and the liver regen them. I can post information about it if you think you could use also that.

P.S: If you have any question ask in comments. I don't bite and I love this!

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  • $\begingroup$ A very informative post. I'm still reading through it, but how do you think the bird can "inhale and exhale" at the same time? It has one throat the air can go in and out of. Inflating one airsac to draw in air while you deflate another to exhale air would just move the air from one airsac to the other as that's the lowest resistance for the air. One thing that might limit bird-lung efficiency for larger animals is the dead space of your throat. An air-sac can only suck in as much volume as it's size, while full lungs pull in the full size change of the lungs reducing the effect of dead space. $\endgroup$ – Demigan Apr 6 '18 at 21:38
  • $\begingroup$ @Demigan, You have right, I've expressed myself bad. They can't inhale and exhale at the same time, but using their air sacs they can simulate that. While inhale, the 50% of air is used to get oxygen and is stored as CO2, the another 50% is stored as O2 in air sacs. During exhalation, the 50% air with O2 is consumed and exhaled while at the same time the another 50% sacs with CO2 are just exhaled, effectively being able to get oxygen all the time (we don't get O2 while we exhale, they do). I'm sorry but I didn't understand that about dead space. $\endgroup$ – Ender Look Apr 6 '18 at 23:11
  • $\begingroup$ So rather than push all the air through at once, you store some and push it through during exhalation? Just FYI, lactic acid does not damage the cells. It has long been thought so as whenever lactic acid was present so did muscle pains, but tests showed that your cells suffer no ill effects from the lactic acid, it just happens to coincide with the work you did and because of that the amount of pain you might experience. Unfortunately its rather hard changing something relatively minor that is being used in textbooks and sports everywhere. $\endgroup$ – Demigan Apr 7 '18 at 12:57
  • $\begingroup$ @Demigan. Birds) Yes, birds do that and it's seem that works for them! (And that is good, because birds consume a lot of O2 while flying, for being exactly, they are the animals which consumes more kcal per kilogram of body). Lactic) You have right, I've just do some research and I found that also, H<sup>+</sup> is produced during lactic fermentation but also consumed producing ATP. I'm sorry. But if that is true, why it produces acidosis? Maybe only lactic acid produced from neutral glucose produce <sup>+</sup>? $\endgroup$ – Ender Look Apr 7 '18 at 15:53
  • $\begingroup$ I don't have my books right now, but if I remember correctly Lactic acid is the anearobic method to quickly create extra ATP, but at the expense of the normal aerobic energy cycle by transforming pyruvate to Lactic Acid. After the body gets rest, the Lactic acid that hasn't been transported to other cells for processing will be turned back into Pyruvate with ATP, then normally cycled to generate ATP (or rebuild into Glucose and brought back for fat storage). I once heard but never saw traces again of muscles that directly burn Lactic Acid, the Heart muscles being the prime users. $\endgroup$ – Demigan Apr 11 '18 at 16:00
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Unsure of the other features, but for efficient lung structure I usually look to birds: http://people.eku.edu/ritchisong/birdrespiration.html.

Also, horses have an interesting mechanism by which they store oxygenated red blood cells in their spleen (up to a third of their total apparently), which are circulated when exercising. Like a natural form of blood doping.

A combination of the two would allow for efficient continuous oxygenation and bursts of fantastically high oxygenation. Having excess stores of blood may also help with continuing strenuous activities after sustaining wounds, and could also allow for extended activity in airless or toxic environments compared to humans. Hit by mustard gas and our supersoldier could simply cease breathing for a few minutes and survive off oxygenated blood stores.

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  • $\begingroup$ to clarify birds have small stiff lungs compared to mammals and no diaphram that is becasue their lungs don't expand or contract. Instead have air sacs that expand and contract moving air through the lungs, they are arranged in such a way that air is only moving in one direction through the lungs maximizing exchange. $\endgroup$ – John Apr 4 '18 at 13:45
  • $\begingroup$ Thanks for the clarification, that's very helpful. What I couldn't work out is whether having bird-like lungs would allow for a rigid fused ribcage which would have obvious defensive benefits. $\endgroup$ – Ynneadwraith Apr 4 '18 at 14:26
  • $\begingroup$ actually many organisms with air sacs have rigid rib cages it actually makes the air sacs work better since they operate by muscles pulling directly on the air sacs. note air sacs and lungs will take up more space than human lungs but you can disperse them around a bit since they don't need a diaphragm. $\endgroup$ – John Apr 4 '18 at 14:41
  • $\begingroup$ Perfect :) even more suitable for our supersoldier. Barring the benefit of a solid ribcage, a dispersed system (with redundancy) would be harder to significantly damage. $\endgroup$ – Ynneadwraith Apr 4 '18 at 20:51
  • $\begingroup$ As a side benefit air sacs still work even if one gets punctured, unlike mammalian lungs. $\endgroup$ – John Apr 5 '18 at 1:21
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Regular, Human Lungs

Homo Sapiens are already the world champion long distance runners. We have an extremely efficient respiratory system and only a few other species come close to matching it.

Humans at high altitude tend to develop lager lung capacity, so your super soldiers could have lungs larger than normal. My lungs, for example, have 150% the expected volume for a man with my age and height.

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  • $\begingroup$ On one hand this seems like a good answer. On the other, isn't human capability based on it's muscles, posture, skeleton build and ability to sweat rather than it's lung capacity? As far as I know the lung capacity of a variety of species can increase by going higher up in the mountains, so it's not exactly a perfect answer. $\endgroup$ – Demigan Apr 5 '18 at 20:58
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Well the most obvious solution is the use of gills. Gills essentially work by maximizing surface area of the bloodstream to the water, making replenishment of oxygen into the fish immediate and not requiring breathing or any such mechanism. The downside of this being that a creature with gills would need to constantly be in movement. Staying still would feel like holding your breath.

Gills would also have the disadvantage of being a weakpoint. It could be somewhat protected, but air must still enter and exit freely and easily, so aside from a mesh of bone, there can be little protection. Having a bucket of water thrown at such a creature would almost certainly cause water to coat the inner linings and prevent that creature from breathing properly. Assuming such a creature is superhuman, oxygen intake is going to be that much more important.

However, perhaps both these issues can be superseded. Requiring that the human is always in movement can be somewhat reduced somewhat by allowing the possibility of having a gill/lung hybrid. Air could still easily enter and exit, but with a small inner pouch that allows air to remain and therefore allowing the creature to move very little if not at all.

For what concerns the weakness to being doused with water, this can be remedied by using many small gill/lung hybrid glands all over the body near to major arteries such as near the hips, on the chest, below both armpits, etc. Dousing one such gland with water would not totally inhibit the creature, assuming the blood system is shared throughout the body. You'd have to completely submerge the creature in water to prevent it from getting oxygen, but the same could be said for us as well.

In addition to this, such a creature could get oxygen distributed far more easily to the body, and again, for an active creature as this, the more oxygen intake the better.

To prevent infection from dust, there would likely be eyelash-like hairs covering the entrance/exit of these glands. The glands would also naturally be angled such that standing naturally causes water to drain from it to prevent pneumonia type diseases from forming when exposed to water. Water would still likely often enter these glands, but this would not be a serious problem considering the sheer number of these glands on the person. However being half-way in water would mean breathing half as efficiently, so if you're looking to add a weakness, requiring these creatures to wade through water might put them at a disadvantage.

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  • $\begingroup$ There's a reason that land-living organisms evolved away from gills and towards lungs. $\endgroup$ – Jack Aidley Apr 4 '18 at 13:36
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    $\begingroup$ gills don't actually work in air, the tight spacing that makes them efficient also makes them collapse in air, not to mention gills are less effective to begin with just becasue air contains a lot more oxygen. $\endgroup$ – John Apr 4 '18 at 13:50
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    $\begingroup$ Assuming you could engineer air-based Gills, I would use these as a secondary breathing system. Put a mostly watertight membrane or hydrophobic membrane over it to protect it, and have muscles that can pull the gills closed when not necessary/lethal gasses are around/you are under water. When you start doing hard work, you are likely moving a lot and pushing the air passed the Gills. If you are wearing a suit you can even let the suit blow air through at higher speeds for accelerated oxygenation/higher O2 content air. $\endgroup$ – Demigan Apr 5 '18 at 10:40
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Use a higher degree of anaerobic respiration.

It is a mechanism that is already existent in humans and our muscles use this all the time when we have sudden jumps in the amount work we do, or when we have insufficient oxygen. It is the fastest form of getting energy, long before your aerobic metabolism can adjust to any load.

See chapter 3 of this paper:

This property allows for shortterm performance far exceeding the levels that can be handled aerobically.

Your super-soldier should have a stronger hart and liver to allow for faster transportation and processing of the resulting lactate. He will also have bigger blood-vessels. This way he will be able to sustain the anaerobic reaction much longer without even needing to start breathing more.

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So there are some great answers on this post already but I feel like there’s a few simple things that may have been overlooked.

First off, humans can do endurance better than just about any creature on the planet already, so instead of major changes go for optimization! Other posts have already mentioned more hemoglobin to carry larger amounts of oxygen in the blood. Keep going with stuff like this. Larger lungs with more surface area means more air capacity and faster diffusion of oxygen into the blood and carbon dioxide out of the blood. A larger and more powerful heart will have a greater stroke volume, allowing for oxygen to be delivered to muscles and for waste products, like the very problematic lactic acid, to be taken away. More efficient oxygen extraction would also help. The average human only extracts a small percentage of oxygen from the blood, meaning that when you exhale there is still significant oxygen in your exhaled breath. Make your super humans extract a much higher percentage of the oxygen from the blood and that will easily double or triple their endurance.

As a secondary improvement, add enzymes to your super human’s muscles that break down metabolic waste at a much higher rate. This doesn’t directly help the respiratory system, but it will greatly improve endurance because once too much metabolic waste builds up too high you’re muscles will stop no matter how hard you push yourself.

So to summarize, bigger lungs with more surface area, stronger heart, more hemoglobin (not too much though, the blood will be too thick to pump!), more efficient oxygen extraction, and enzymes that catalyze metabolic wastes and cause them to break down much faster!

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    $\begingroup$ As mentioned in another comment to Ender Look, Lactic Acid is not a problem in muscle's. Lactic acid is formed as an emergency measure from pyruvate instead of it being used for the normal cycle. This produces less ATP but it does so faster and requiring no (or much less, not sure) oxygen. While old textbooks and your local gym coach will tell you that the acidity is bad for your muscles, it has already been discovered that muscle pains/failure and lactic acid buildup are coincidental, but not causal. Muscles are well capable of handling the acidity of lactic acid without problems. $\endgroup$ – Demigan Apr 11 '18 at 15:55
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    $\begingroup$ That’s true, lactic acid’s role in fatigue in uncertain. I edited it for just metabolic wastes in general. $\endgroup$ – Nick Apr 11 '18 at 16:04
  • $\begingroup$ Enzymes for metabolic wastes sounds like a good idea, but maybe we could look at other stuff as well. Muscles as a rule have relatively little room for cell activity outside of it's contraction duties, so also less room for enzymes. Perhaps we could look at the other side of the coin: Transport. Both the blood system and the lymph system supply the muscles and transport (temporary) waste away. The ability to transport more would be extremely useful, especially when it becomes possible to let other cells take over processes for the muscles and then transport the result to those muscles. $\endgroup$ – Demigan Apr 11 '18 at 16:38
  • $\begingroup$ That’s true, maybe put the enzymes in the blood so that they don’t take up room in the muscles. That way you decompose the waste as you remove it from the muscles. $\endgroup$ – Nick Apr 11 '18 at 16:40
  • $\begingroup$ Wouldnt that be counterproductive? You now have to make room for enzymes and waste material in the bloodstream where you could put bloodcells that carry oxygen and materials to the cell and remove its waste. Perhaps a few dedicated non-red bloodcells that have superior waste carrying capacity would be an option if those cells bring it to nearby cells that work through it. $\endgroup$ – Demigan Apr 11 '18 at 17:53

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