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.

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?

> what's the optimal gravity for running if it's not 1.0 Earth?

Is "optimal running gravity" the gravity under which you'll run the fastest, or the gravity under which you'll have suffered the least amount of physical damage after running for a fixed distance/time?

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.

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.

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.

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.

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.

Who cares about sprinting, I can't wait for the lunar pole vault.

Olympics on the Moon? Maybe in 2020 according to one futurist of the past...

http://usbornepublishing.tumblr.com/post/60362087283/it-is-t...

(Scroll to the end specifically for the Olympics.)

In my amateur runner mind, that's where I spend the most time on technique. Balancing the effort waves ensuring everything goes forward and not up nor down. Faster means inertia, means lighter if not done appropriately, which require to tweak your approach.

is the solution stairs?

It would be interesting if you could achieve a faster speed on the moon running up a flight of stairs than running on a level lunar surface.

Alternatively you could 'angle' the stairs on a level surface (think saw-tooth pattern) and translate that upward energy into forward energy.

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.

> 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.

Interestingly, you've hit upon the popular hypothesis that flight actually evolved via the wings providing downforce enabling faster/vertical running up trees.

So, we need longer feet. Or longer shoes.

More legs!

Maybe some form of spoiler :P?

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.

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

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

[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.

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 ...

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.

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

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.

> If you tripped and fell at 35-40mph you could seriously injure yourself.

To be fair, this is quite true at walking speeds as well. Falling is bad. I passed out from dehydration once while standing still; I ruptured my spleen in the fall and almost needed surgery to have it removed (thankfully, it healed while I was under observation).

> "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?

> 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.

That's my understanding as well. The title makes no sense and seems very click-baity.

"Our simple projections indicate that muscle contractile speeds that would allow for maximal or near-maximal forces would permit running speeds of 35 to 40 miles per hour and conceivably faster"

So essentially if human physiology worked differently than it did, we could theoretically run much faster. Not a useless result, but not really anything as exciting as they make it sound.

Yea that was my read too. Of course you have more force on one leg - all your weight is on it and there's less forward momentum.

If you could get all that force into running stance...that's like saying michael jordan has a great vertical. If a runner could apply that same vertical while running top speed, he could leap really far.

More about Usain Bolt's peak performance: http://www.dailymail.co.uk/sciencetech/article-2378698/Scien...

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.

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…

nah, not going to do that

it hurts my knees anyway