not a physics major wrote:
John Clendon wrote:I think the IAAF rule is getting at "shoes that return more energy than was put into them".
Picking arbitrary numbers here, if the foot pushes against and compresses the shoe with 50N, and the shoe returns 55N. That is the unfair advantage.
Nike and Adidas with Lunar and Boost are trying to return the same amount of energy as the initial push.
Is it even possible to return more energy than what is put into it? Wouldn't that be the premise of Flubber?
It's not a question of returning MORE energy than what is put into it like Flubber, but rather returning more energy than other materials do under the same pressure. But think about this: a spring can be compressed easily under your weight alone without an effort on your part to compress it. If your weight alone can compress it, then it will stay compressed. However, once you begin to lift your foot and reduce that weight until the spring begins to decompress, THAT'S where the energy return takes place. Prior to that it is simply stored energy in the compressed spring. As far as I know, actual springs are illegal in any running or jumping sport as an unfair advantage. But EVA, Boost and other midsole materials, as well as rubberized running tracks, are more subtle in their energy return. In a totally "fair" world, all athletic records would be set at sea level on identical surfaces, weather conditions (no wind), and with identical equipment, but that's simply not practical. As for the Boost "advantage," it IS my own non-scientific perception while running that Boost provides a perceptible increase in energy return--especially on hard surfaces--over the energy return provided by any typical EVA midsole shoes I've ever worn. For doubters, I say, try it and I think you'll feel it. Is it an unfair advantage? No more than EVA was when it was first introduced. And not when it is easily accessible by all runners. Of course, price point does become a possible issue, but not excessively when there are other shoes besides Adidas Boost out there that cost as much or more. If you want to argue the price point issue, we could discuss cycling, as well. To get the best racing bicycle, you have to pay for it, and it ain't cheap.