Images Cited

http://www.runningshoesguru.com/wp-content/uploads/2017/08/Nike-Zoom-Vaporfly-4-Pair.jpghttps://i.insider.com/61095ae2c31de7001849f7ae?width=700https://hips.hearstapps.com/hmg-prod/images/sp20-footwear-viperfly-spike-original-hd-1600-1580914710.jpg?crop=1.00xw:0.893xh;0,0.107xh&resize=1200:* https://www.nytimes.com/interactive/2019/12/13/upshot/nike-vaporfly-next-percent-shoe-estimates.html