Ooooh, interesting- I’ll take a read, thanks!

I’m guessing like most things of this nature, you’re likely to have super-responders, responders and non-responders?

Yes, most of the studies show there is a very large individual variation. The original 4% figure and similar studies were an average of something like 1-7% across runners.

Also interestingly, the shoe in this record uses much less carbon than past shoes, both saving weight and allowing even more super foam where much of the energy return comes from. Though there so much variance in shoe design and materials there are only theories on how much comes from the plate vs foam vs stack height vs weight vs other factors.

I read somewhere that the carbon plate is more to stabilize the shoe, that with only the foam the shoe would be very unstable.

Yes, that's correct. There's a mistaken belief that it's the major source of performance improvements. It plays a role, but the bigger gains come from the stack height (limb lengthening effect) and the energy return of the foam. But that leads to very unstable shoes. The carbon gives rigidity to balance this out.

Maybe even placebo effect?

Quite possible there's a psychological benefit from super shoes, they certainly feel fast. Though there are enough plausible mechanisms it's unlikely to be the major factor.

So you think the Vaporfly prototypes Kipchoge wore in 2018 placebo'd him into crushing the world record by 78 seconds?

There's an almost inhuman amount of mind over matter psychology when it comes to endurance running. Unless you can duplicate reality multiple times and swap out the shoes without anyone knowing to do properly scientific testing, we can't know for sure what did it. (The shoes probably helped.)