
Human running speed of 35-40 mph may be biologically possible - jpalacios
http://blog.smu.edu/research/2010/01/21/human-running-speed-of-35-40-mph-may-be-biologically-possible/
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IvyMike
I've always been curious: in an enclosed stadium on the moon, would humans run
the 100 yard dash faster or slower?

I think the first reaction people have is "faster, since you weigh less". But
I think the answer is slower, because you would actually be near-floating and
contact the ground less.

I got into a fight with people on ask.metafilter when I asked this same
question, so I had to let it go. But still I hope someday the Olympics are
held on the moon so I can get my answer.

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jcrites
You would certainly accelerate much more slowly, since the upper limit of
acceleration is bounded by your friction with the ground, which is bounded by
your weight, i.e., your mass times gravity.

What's not clear is whether you could reach a faster peak speed. I think it
would be tough to reach a fast speed since your joints would need to oscillate
rapidly in order to push off ground moving as fast. And each time you push off
the ground you'd achieve less force, due to the friction thing. To summarize,
I think I agree with you that humans will run more slowly in a low-gravity
environment.

An interesting parallel question is: under 1.3, 1.5, or 2x gravity, how much
more quickly could you run? And what's the optimal gravity for running if it's
not 1.0 Earth?

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omegant
Would a 2x gravity be similar to running with a 100 pounds backpack? Then I
guess it's going to be substantially slower than 1G running.

~~~
recursive
No. The runner still has the same mass, so accelerating takes the same amount
of energy as 1x gravity. It's like shifting to a higher gear on your bike.

~~~
crystaln
Not exactly. Horizontal acceleration takes the same amount of energy. The mass
of the body must also be supported upon landing, which obviously takes more
energy with more gravity.

~~~
jcrites
Interesting. So it will feel like your normal weight in the horizontal
dimension, but it will feel like wearing a 100-pound backpack in the vertical
dimension.

Your ultimate running speed then depends on how strong you are. That 100 pound
"backpack" will push you into the ground and give you far more acceleration
than your normal weight would allow: it will feel like you have ultra-
traction. But when you push to the side and accelerate your body, you're only
accelerating your normal body weight.

Marathon times will likely suffer, but perhaps some short sprints will be
faster in gravity over 1g.

~~~
crystaln
Exactly, although inertia might be more correct, particularly for the
horizontal dimension.

More gravity, to a point, will increase running speed. Would be interesting
for someone to calculate the optimal gravity for running.

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arjie
Title had me confused for a bit. The article says that it was previously
thought that the amount of force a limb can apply to the ground was the
limiting factor in speed. However, it turns out that the actual limiting
factor is how fast the muscles can apply that force. If muscles could apply
the full force in the fraction of time that feet touch the ground, then that
person would achieve those speeds.

Interesting result.

~~~
ars
> If muscles could apply the full force in the fraction of time that feet
> touch the ground

Or if they could touch the ground for longer. We need human mounted wings to
provide some downforce :)

Or more realistically an elastic belt strapped to the runner, and running on a
track underneath them.

~~~
ajuc
So, we need longer feet. Or longer shoes.

~~~
bdg
More legs!

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blisterpeanuts
More frequent steps per minute (higher frequency gait) might enable higher
speeds because of more contact with the ground and less vertical motion. More
contact with the ground provides more friction with which to hurl the body
forward. However it also requires more energy.

I've modified my running gait to about 186 steps per minute to reduce vertical
motion (about 6 cm as measured by the PT at the runner's clinic). I'm still
building up the muscles to maintain this gait longer than a minute or two,
though.

It would be interesting if a new and improved (or reconstructed Paleolithic)
method of running is developed that would enable the average person to reach
speeds of 35 MPH (56 KPH) or even faster.

If I could run that fast, I'd get rid of my car and run to work every day.
They'd have to have running lanes, maybe even issue speeding tickets to
runners who race through a school zone. Road rage would take on a whole new
dimension, as well. The economy would be transformed as millions of cars are
discarded, gasoline consumption plummets, and people become thinner and
healthier.

~~~
Apofis
That's some wishful thinking right there, I love it.

~~~
blisterpeanuts
Yup I waxed a bit hyperbolic there, but wouldn't it be great?

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Silhouette
[2010], but fascinating all the same.

If you'd asked me how fast an elite sprinter could run today, I would probably
have thought of running 100m in a little under 10s, but I don't think I would
have connected that mentally with the idea that Usain Bolt runs almost as fast
as a car on our 30mph streets, albeit very briefly.

~~~
agumonkey
I'm as astonished to think that marathon runners can sustain 20 km/h for 2
hours. 20 km/h is my average speed on bike ...

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ck2
Wind resistance has to be a factor after 25mph, I mean it is on my electric
bicycle.

And holy cow, even 25mph is crazy fast, 35? If you tripped and fell at
35-40mph you could seriously injure yourself.

I think I have a good question for the xkcd q&a site: how fast could Usain
Bolt run on the moon (ignoring the oxygen problem).

Ah I see someone beat me to the moon problem. Here's another thought, without
strong gravity to help return mass to the ground, running is probably much
harder.

~~~
maxerickson
This analysis says Usain Bolt expends >90% of his energy on drag:

[http://iopscience.iop.org/0143-0807/34/5/1227/article](http://iopscience.iop.org/0143-0807/34/5/1227/article)

(That is, yes, you are correct.)

Answering my own question, he took 41 steps when he set the world record.

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faitswulff
> "Despite how large the running forces can be, we found that the limbs are
> capable of applying much greater ground forces than those present during
> top-speed forward running.”

Correct me if I'm wrong, but if they extrapolated this from one-legged hops,
which put all of your weight on a single leg, isn't that more akin to
measuring the ground force from jumping than it is to running?

~~~
ForHackernews
> isn't that more akin to measuring the ground force from jumping than it is
> to running?

The point is that the limiting factor is _not_ how much force the limb can
exert, and that's what was demonstrated by the one-leg hopping.

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aaronbrethorst
More about Usain Bolt's peak performance:
[http://www.dailymail.co.uk/sciencetech/article-2378698/Scien...](http://www.dailymail.co.uk/sciencetech/article-2378698/Scientists-
reveal-Usain-Bolt-energetic-speeding-bullet--reach-speeds-27MPH.html)

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mingabunga
Running on a treadmill (as in this experiment) is quite different from running
on an all weather track as sprinters do. I wouldn't be surprised if they got
quite different results if somehow they were able to measure this on a non-
moving track.

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reubenmorais
I can't see how it'd make any difference for this experiment. They were
measuring ground forces applied by the runners and how fast those forces are
applied, so unless the all weather track has artificial gravity…

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finalight
nah, not going to do that

it hurts my knees anyway

