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A runner has superpowered legs, allowing him to run extremely fast (as in, each of his legs can "push" the ground very fast.) However, he has two different options for how he should run. Should he run in:

  • long, bounding strides; or
  • short dashing strides?

Why?

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    $\begingroup$ @L.Dutch-ReinstateMonica : I think OP just wants to know which technique would be fastest, seems a fairly simple question really, there's nothing to suggest he wants to consider exhaustion & stamina with respect to long distance races. $\endgroup$ – Pelinore Dec 5 '19 at 7:50
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    $\begingroup$ @Pelinore, the use case is vital to define what is best. The use case here is missing. $\endgroup$ – L.Dutch - Reinstate Monica Dec 5 '19 at 7:51
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    $\begingroup$ @L.Dutch-ReinstateMonica a sprinter's gait is optimised for speed and power. A marathon runner's gait is optimised for efficiency. If a superhuman could run a marathon at Bolt's speed, they'd use a sprinting gait to do so, because it demonstrably works at that speed which a marathon runner's gait would not. $\endgroup$ – Starfish Prime Dec 5 '19 at 9:01
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    $\begingroup$ What has this to do with world building? $\endgroup$ – Slarty Dec 5 '19 at 14:34
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    $\begingroup$ @Slarty OP is asking help to refine a super power that exists in their world, seems pretty on topic to me $\endgroup$ – BKlassen Dec 5 '19 at 16:07
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One factor the other answers havent hit on yet is the need to change direction.

If your hero needs to change direction often, not just run as fast as possible, then you will need short enough strides to allow you to be in contact with the ground at a sufficient interval to be able to change direction within acceptable time frames.

Consider if your feet only touch the ground once a second, then you would only be able to correct your direction in a chase once a second. Good luck catching someone who knows how to zig-zag.

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Your runner will be subject to aerodynamic drag. The force of drag is basically this:

$$F_D\, =\, \tfrac12\, \rho\, v^2\, C_D\, A$$

Where $\rho$ is the density of air, $v$ is the speed of the runner, $C_D$ is their drag co-efficient and $A$ is their cross sectional area. If you double your speed, the force of drag will quadruple. When you push off against the floor with your feet, not all the force is going forwards, but some will also be going up. Sprinters are limited with how much forward force they can impart per stride without slipping, which is why they use spiked shoes for extra grip. To get double the speed, then, you'll need to more than quadruple the force your legs impart and you'll either end up springing much higher into the air (your "bounding gait", perhaps) or skidding on the ground. Firing yourself into the air is bad, because it will take time for you to come back down again (unless you have super-gravity-enhancing powers), time in which drag forces are continually acting to slow you down.

What you need to do then, is:

  • Wear suitable shoes for super grip. Studs on grass (but you'll still be very limited on such soft surfaces), spikes for asphalt, grippy rubber shoes for hard, smooth surfaces. One shoe won't suit all purposes. You'll never catch a bad guy in a dune buggy racing over sand.
  • Wear a highly aerodynamic helmet (like one of these, the sort that time trial cyclists wear), ideally with a visor because super speed bugs to the eyeball will put you off your stride. You may finally also have a good excuse to wear a skin-tight super-suit too, to keep your skin friction nice and low and try to keep your drag coefficient as low as possible.
  • Get down low. Look at the pose sprinters are in when they start running. You'll be moving more like a conventional tetrapod, all stretched out, though your forepaws hands won't necessarily be used nearly as much. Keep your cross-sectional area down to minimise drag.

So the answer is probably going to be: (c), neither of your two options but more like a low down speed scramble, whilst wearing a funny outfit and carring a bag of shoes.


ETA: if you've got super strong, super fast legs then the way to go really quickly is to get a bicycle, you know. Much more efficient, no worries about punting yourself into the air with each step or what shoes to wear, and with an aerodynamic fairing you'll have far fewer drag issues. Also, I don't recall anyone else talking about a super-cyclist before, so you could be the first!

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    $\begingroup$ Mumen Rider would like a word with you. $\endgroup$ – pjp Dec 5 '19 at 15:11
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    $\begingroup$ @pjp I stand corrected. $\endgroup$ – Starfish Prime Dec 5 '19 at 15:13
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It depends upon the characteristics of the superhero.

Consider The Incredibles. Dashiell Parr (Dash) has the superpower of running fast, by moving his legs very rapidly. Bob Parr (Mr. Incredible) on the other hand is incredibly strong.

Dash can maintain higher speed by frequent contact with the ground. Whereas Bob would move faster by maximizing thrust with each step, and using a loping stride.

It appears you are describing a superhero with more like Dash than Bob, so the short-dashing stride would give a higher speed.

The documentary shows the short stride clearly in the case of Dash. Bob is shown running with a longer stride, but never really shown making a series of great leaps, though one suspects he could leap tall buildings in a single bound.

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Something I'm not seeing mentioned in the other answers is the integrity of the ground under our hero.

If he uses long strides, his steps put more stress on the ground under him and runs the risk of spraying asphalt shrapnel into the faces of everyone standing behind him. Ricochet puts people to the side at risk as well.

Shorter and faster steps make his feet more like the tires on a car, which don't usually have dangerous spray unless they are on gravel.

I think this, along with a bunch of the other answers gives your hero some things he has to think through. There is no one answer, and he will have to adapt to each situation.

Also, the gravel thing is almost his "kryptonite". Fighting in a gravel pit surrounded by innocents basically guarantees he can't use his powers.

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  • $\begingroup$ I actually considered referring to this in my answer, then I considered that Dash was able to run on water. For the Bob Parr superhero, this would certainly be a consideration. $\endgroup$ – Gary Walker Dec 6 '19 at 12:58

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