Recent Improvements in Marathon Times Are Not Physiological

to the editor: October 2019 saw Eliud Kipchoge run the marathon distance unofficially in under 2 h, and Brigid Kosgei break Paula Radcliffe’s 16 yr-old marathon record both in carbon fiber plate (CFP) shoes. Current men’s and women’s world records in the half- and full-marathon have all been broken by Nike athletes in CFP shoes, raising concerns that the introduction of this technology leads to a distinct nonphysiological advantage to Nike-sponsored athletes. For example, Javier Guerra chose to break his Adidas contract to use a Nike CFP shoe and qualified for Tokyo 2020.

Laboratory studies have shown improved running economy (RE) with CFP shoes (3). Unpublished data from our laboratory shows a 2.3% improvement in a female runner wearing CFP shoes during three 10-km trials (39:08 ± 00:29 min:s) compared with three 10-km trials wearing her preferred non-CFP shoes (40:03 ± 00:20 min:s). In another unpublished study from our laboratory, we tested an East African athlete (a current World Record holder) running on a treadmill at 21 km/h, and a CFP shoe elicited a 2.6% improvement in RE compared with his preferred non-CFP shoe. The recently released Nike Alphafly shoe has been suggested to improve RE by more than 5% and potentially, the men’s marathon by 5:30 (min:s) (4), which is comparable to the performance benefit of doping with erythropoietin (1, 2). Recent improvements in marathon world records are not physiological as implied in the Viewpoint of Joyner et al. (5) but rather technological. Current rules are therefore no longer fit for purpose, requiring revision to safeguard the integrity of sport.