Why not downright high tensile strength springs in running shoes?

They got invented long time ago.

Not 100% sure if they were successful.

https://www.amazon.com/Seakyland-Unisex-Jumping-Bounce-Adults/dp/B07HMTMKRT/ref=asc_df_B07HMTMKRT/?tag=hyprod-20&linkCode=df0&hvadid=312140914202&hvpos=&hvnetw=g&hvrand=12086681787700230338&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9013528&hvtargid=pla-604443248828&psc=1

It's been done, and flopped:

https://runningmagazine.ca/sections/gear/shoe-review-enko-g4/

Also, wtf:

https://www.nike.com/launch/t/ispa-road-warrior-clear-jade

Also, double wtf:

https://www.balenciaga.com/en-us/x-pander-sneaker-black-809857346.html?targetid=pla-1443025210767&location=9002488&gclid=CjwKCAjwzOqKBhAWEiwArQGwaOQsp3-SzGuNuIne3WIRICMgKBO77ZSRzDnVwRcRrvxrH2KLvnc8ZRoC6xwQAvD_BwE

Then what exactly about a carbon plate makes it better than a spring in returning stored energy, assuming that that is how it is working to provide the few percent of economy benefit?

The plate allows for a longer lever arm across the foot and ankle.

Plus, I imagine it's much more lightweight than any attached spring mechanism.

Not a physicist or biomechanist.

Those are probably too heavy… the return of the stride becomes inefficient

Nick Symmonds failed to run a 5 or 6 minute mile in spring stilt shoes and he got roughed up several times falling. Those shoes are said to allow speeds of 20mph, which is as we know, unimpressive, unless it can reasonably be maintained

sproingo wrote:

So, if carbon is so great because it’s efficient at returning stored energy when compressed, why not just place short, high tensile strength springs with a high spring constant under or inside the soles? Wouldn’t they be the most efficient in returning stored energy? The IAAF rules only seem to require wide availability and, as of more recently, a 40mm stack height budget.

It's an optimization problem. Stiffer isn't necessarily better. Think of a tennis racket, baseball bat, or golf club. If it's too stiff you don't get that "trampoline" effect. Likewise if it's not stiff enough that isn't good either. You need something that will have the right time response (tuned) for the problem at hand. The optimal spring for running will vary individual to individual and that's likely why some respond better than others. I'm sure there's some correlation between shoe size and optimal stiffness and I'm sure they are compensating for that. But if you're size 11 and weigh 120 pounds and your foot is on and off the ground in 0.X seconds you likely need a different stiffness than someone who is size 11 and weighs 160 pounds. Maybe we need shoes that are individually tuned. You want a spring that will compress for a similar time that the foot is landing and then start to extend as you're pushing off.

because despite what rojo the carbom isnt a spring. the foam stores the energy and carbon helps direct it in the right direction...

How about taking a pair of Alphafly's and removing the airpods and puttiing a spring in their place?

As noted, it is actually the foam that is the spring. I don't think it is clear exactly what the plate does, other

than it does seem to be needed.

As above, getting the spring part right is actually pretty complicated. Trying another way to explain it.

You foot hits the ground with what, like 4x your weight or something, and that is when the spring will

compress. As soon as that force lessons, which happens well before you are pushing off, the 'spring'

will start decompressing. To take the extremes, if it fully decompresses well before you start your

push off you won't get any energy back. If it decompresses after your foot leaves the ground you

won't get any energy back either.

One explanation that I've heard for why most elite runners have about a 180 cadence is that that

matches what is needed to make best use of the main natural spring used in running, the Achilles tendon.