Ho Hum wrote:
I think the issue here is that the rule doesn't really make sense, i.e. adding more stack doesn't make this shoe any faster. I mean, weight does matter to a point, and this weighs over 9 oz.
Somebody else alluded to this but this is a fundamental point. These products (from all brands) use super surface-tension, easily compressible, foams. The need to so they can cushion but still enable maximum force transfer from the foot to the ground surface.
So all the hype and panic around stack heights is kind of stupid because there is a point of diminishing returns with respect to this.
1) Weight (as you pointed out) - more material, no matter how light = more weight
2) Geometry based stability (someone else pointed out) - at some point if a midsole made of soft material is so high off the ground it simply will become inherently unstable - even when running on a flat surface in a straight line
3) To my point above, what is happening with the foam during the foot-strike is that it is easily and quickly compressing under the athletes applied force. The ideal scenario is for the foam to be basically packed out as firm as possible right under the athletes foot in the fractions of a second prior to pushing off. If this happens the compression process has provided the cushioning and the resultant compressed foam provides the platform for the maximum amount of energy/force to go into the ground - the number one determining factor in how fast you run (Newtons third law). All of this needs to happen in the 200-300 milliseconds that the foot is in contact with the ground. If it doesn't meet these conditions the shoe isn't as efficient as it should be.
So just pumping up a stack height as high as possible is kind of meaningless. Because at some point there simply isn't enough foot-strike time for the foam in the shoe to be compressed down to it's optimal level. When that happens the effect can be dramatically reversed as the amount of wasted energy/force per step can be significant - especially over a marathon and the 20000+ steps even for elites.
Maybe that is why despite an illegal shoe we only saw 2.09.22 which by todays standards is a very average performance?