"The results were somewhat unexpected. The bending of the carbon fiber plate stored and returned energy at a rate of 0.007 watts per kilogram with each stride. In comparison, the squashing and unsquashing of the thick ZoomX foam returned 0.318 W/kg—more than twice as much as either of the other shoes, and about 45 times more than the plate. So the shoe definitely functions like a spring, but in this analysis it’s the foam midsole rather than the stiff plate that makes almost all the difference in the shoe’s contribution to energy savings".
This is from Alex's Outdoor Magazine Article from November 20th, 2018 (
https://www.outsideonline.com/2367961/how-do-nikes-vaporfly-4-shoes-actually-work
).
I've seen other people post about the fact that it's the foam that acts as a spring and not the "spring" plate, but a lot of people don't seem to be able to get their minds beyond the label of "spring plate". The plate creates stiffness in the shoe that acts in the same way as a spike plate. It doesn't spring you forward in any way. So, the question then becomes, if stiff shoes (plate or not) shouldn't be banned, do you now want to ban foam that is too springy? Tracks that are too springy? Outsoles that are too grippy? Until a shoe actually runs for you or actually gives you MORE back from your push off than you put in, then we should let technology continue to improve (to both improve our running times and our running experience). Or we can have "natural" competitions without any shoes at all. Bring back grass tracks for these competitions?