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=Other Breaking-2 Shoes=
Nike's highly publicized attempt to break the 2-hour marathon was documented in the National Geographic "breaking 2" (freely available on youtube.com). That failed attempt used the Nike Vaporfly Elite, a shoe you can't buy. This Vaporfly uses the same ZoomX foam and a carbon fiber plate in the midsole as the Vaporfly Elite. There is also the [[Nike Zoom Fly]] which looks superficially identical to the Vaporfly, but is radically different and vastly inferior.
=Is It Really Faster?=
A study [https://link.springer.com/article/10.1007/s40279-017-0811-2 "A Comparison of the Energetic Cost of Running in Marathon Racing Shoes"] looked at the performance of the similar prototype shoe to the Nike Vaporfly. This study included researchers working for Nike, as well as the University of Colorado, and it used a shoe that not actually the Vaporfly, so use caution in interpreting the study. The picture below gives some insight to the construction of the Vaporfly, but also suggests some differences from the prototype which appears to have a full with carbon fiber plate.
[[File:Nike Prototype.jpg|center|thumb|300px|The prototype Nike]]
The prototype was compared with the Nike Zoom Streak 6 (NS) and the Adidas adizero Adios BOOST 2 (AB). It's nice to see that they disclosed the actual shoes they compare it to. The researchers added small weights to the two Nike shoes so they were weight matched with the Adidas. A mechanical check showed that the prototype shoe was twice as well cushioned as either of the other shoes, deforming 11.9mm versus 6.1 and 5.9 mm. They prototype also had more bounce, returning 87.0% compared with 75.9% for the Adidas and 65.5% for the Steak. The study then compared the [[Running Economy]] of sixteen male high-level runners in the three different shoes. The runners have a [[VO2max|VO2max]] of ~72, which is translates to a marathon time of about 2:20. They tested them at 14 kph (6:53 min/mile), 16 kph (6:02 min/mile), and 18 kph (5:22 min/mile), all below the [[Lactate Threshold]] of the runners (4 mmol/l, which is good enough for this study.) The running economy of the prototype shoe was 4% better than either of the other two shoes, which had similar running economy. The study noted that the prototype shoe was slightly better for rear foot landing runners (~4.7%) than the forefoot landing (~3.6%).
=Update After 100 Miles=
Normally, I would give an update on a pair of running shoes once I'd put rather miles on them. However, the vapor fly as something of a reputation for fragility, so I wanted to track its progress carefully. Even after this short distance, there is some evidence of the foam midsole braking down. If you look at the profile picture below, you can see some increases in the midsole appearing, and there is a noticeable indent under the ball of my foot. On the underside of the shoe, there is only a small amount of abrasion on the exposed foam. The hard rubber outsole (the black areas) are completely unchanged, suggesting that they are surprisingly hard wearing. The grip has improved over the course of the 100 miles. The main abrasion area on the exposed foam midsole is on the outside rear edge, where I occasionally catch my heel on steep descents. It should be noted that my running biomechanics are fairly efficient, and I'm typically quite gentle on my shoes. The upper is doing fine, even where I've cut open the toe box.
