# How fast could a 3.2m tall, 380kg human run?

Over the past one and a half years, together with your friend, I am writing a book about anatomically plausible superpower (artificially created form of a person, in all superior modern people, both in physical and intellectual plan), as well as what could civilization of these extraordinary creatures .

Thinking out the physiology of these super supervisors, I thought about how quickly they could run given the fact that their average height is 320 centimeters, and their average weight - 380 kilograms?

So the average speed of an ordinary trained person in running on distant distances is about 15-18 km / h, but how quickly they could run?

• I would say not at all. I doubt our skeletal system would be able to handle the stresses of running when scaled up like you propose.
– Aron
Apr 9, 2021 at 13:47

With the legs twice as long, they would have more or less double stride. Keeping muscle power ratio more or less the same, you could expect a little less than twice the average human speed.

# But

Legs are important, but muscle speed, stamina, recovery time and coordination are even more important. How fast can an unmodified human run? The current record is around 44 km/h (but any Navajo warrior will tell you that how long can be important too, since they could routinely outrun cavalry horses by the "simple" trick of getting much less winded). So, a doubly-length-legged Usain Bolt could be expected to reach 80 km/h. The average doubly-length-legged human would still sprint no more than 40 km/h.

And if you got cricket muscles into your superbeing, they could move their legs twice as fast. So you start from 20 km/h, double that because they've got longer legs, double again because they've got cricket thighs, and double again because they're Usain Bolt - and end up with 160 km/h.

However, energy expenditure goes up quadratically with speed and linearly with weight, and 10 km/h requires around 833 W of power (2.82 m/s is 10 km/h, 1600m / 2.82 m/s is 576 s, 480 kJ in 576 s is 833 J/s, i.e. 833 W). Four times the mass means four times the expenditure, and 80 km/h is sixty-four times the expenditure; 213 kilowatt of organic power seems unthinkable for a humanoid, and they'd die by heatstroke in a very short while (the larger the body, the lower the surface-to-mass ratio and the more difficult to cool down)

• The Square-Cube Law is Not Your Friend. Apr 9, 2021 at 14:30

It depends.

A strongman has most of his muscle mass in his torso and he's mostly focused on lifting stuff rather than running.

A cyclist has more muscle mass in his legs, but the muscle groups in question do not help overly much if you were to start running. Some of the best cyclists in the world can't even finish a marathon.

A long-distance runner comes close. He's got the right muscle groups trained up, but his muscles are endurance muscles that can generate less force in a short timespan so they aren't as fast.

Short sprinters like Usain Bolt is where it's at. They are trained for speed and have the right muscle types in the right muscle groups.

If you want a specific "they run X m/s" answer I don't think we can help you. We would need to know if they trained for this exact thing their entire life or if they are a more "good at everything" type of superhuman. Even then its going to be hard to make accurate predictions.

The best answer I can give you is "it depends". Your superhumans will not all be the same. Some will be in positions where it's better to be able to run faster, some will need to be able to lift things for a long time, others need to be able to resist cold more and will sacrifice muscle mass for more hair and fat to insulate themselves etc.

It depends on a fair few factors of how these super powers are shaped. Given the average human (male) size of 1.8m and 70kg, if you scaled the height directly (factor of 1.7) you'd get a human sized 3.2m and 120kg. This means your supers have a lot of increased mass, this is to be expected as they need more muscle to keep up with their increased size, but the increase is almost a factor of 3 higher than expected.

Strength

Now I'll compare your super soldiers to strongmen like Hafþór Júlíus Björnsson, one of the heaviest strongmen recorded, with a height of 2.05m and a top recorded weight of 205kg. This is already closer to your numbers, and scaling this up gets very close.

Now how does this translate to speed? Hardly, I'm afraid. There are records of strongmen reaching sprint speeds of roughly 26kmh, but this is over very short distances. Long distances aren't done by strongmen for various reasons, but mostly because of my next point.

Diminishing returns

Scaling up muscle length diminishes their usefulness tremendously, so the concept of bigger = stronger doesn't really hold up. This will be paired with the fact that more weight needs more energy to move, so large muscles are needed. And more muscles equals more weight, meaning even more muscle power is needed, and so on. A lot of the muscle mass of one of these supers will be needed for simply moving around, and won't help for athletic feats like running.

Issues

Due to their size, and the fact that they are created from ordinary humans, I'd expect your supers to have the following issues:

• Brittle: Their bones will be elongated and out of proportion, the average human skeleton simply isn't built for the strain put on by such a tremendous size. So either their skeleton will need to be reinforced or they would simply pull themselves apart. This adds a lot of weight, which isn't muscle mass.
• Tires easily: Moving a large amount of weight requires a large amount of energy. Moving a body of the size you describe will require an exponential amount of energy, which the body stores mostly as fat, which is once again, added weight that isn't muscle mass.
• Weak: Over all, I'd expect these supers to be weak in comparison. They will indeed weigh a lot, and a lot of this weight won't be in the muscles needed to move, and the muscles will have already diminishing returns. This means that they won't be nearly half as efficient in movement as a regular human, for an increased amount of effort. I don't mean they are weaker than a human, but they won't be "Twice as big and twice as strong", rather they might be twice as big and only 1.25x as strong.

Conclusion

Of course the question was about speed, and this is a tough one, as speed does not scale at all like strength does. Rather as I displayed above, the increased weight would diminish speed rather than increase. The only positive thing about their physique would be their increased stride length. You state that longer distance running is 15-18kmh on average, but I think this is already generous. A 10km run is more often done at roughly 10kph. With the added weight and energy requirements of your supers, I would expect this to be more like 8kph or slower for a trained super. Also, I would question whether they have the energy to do such runs often if at all.

• Eeeeuwww you used 70kg first and switched to pounds in the same sentence. That is dirty dirty imperialism. Apr 9, 2021 at 8:01
• @Demigan Apologies, I typed pounds on autopilot as per the reference weights I worked off. But the number was in kilos. I have amended this now, and I apologise for my horrendous imperialistic sacrilege. Apr 9, 2021 at 8:04
• Reading your list of issues I have to disagree. You are listing the disadvantages of Gigantism which is a specific growth disorder. It's like noting the potential growth defects of dwarfism as what would happen if we scaled humans down. You are deliberately saying they'll have a badly formed skeleton, but why would anyone build a superhuman with badly proportioned bones? They would naturally change the proportions to get the most out of it while retaining the human bodyplan. A question still unanswered correctly on this site is "how large could a human healthily get". Apr 9, 2021 at 8:12
• I address this in the list of disadvantages as well, stating that this would happen if scaled up directly. I state at every point that if these issues are addressed, it would add weight to the body. With the fixed given weight being a directly limiting factor, this would leave less room for muscles, meaning a diminished return in output. Apr 9, 2021 at 8:20
• You said "Given the average human (male) size of 1.8m and 70kg, if you scaled the height directly (factor of 1.7) you'd get a human sized 3.2m and 120kg." But this is incorrect. Volume increases at the cube of linear scale so, assuming constant density, the correct mass is closer to 70 kg * 1.7^3 = 360 kg. Apr 9, 2021 at 17:06