#ChonkyBois: When It Comes to Running Shoes, How Thicc Is Too Thicc?

Molly Woodford, MJLST Staffer

Early last November, I wrote a blog post about the developing controversy surrounding the Nike Vaporfly NEXT%. At that time, the IAAF (track and field’s world governing body, which has now rebranded itself as “World Athletics”) had just announced that it was assembling a working group to examine the Vaporfly controversy and “find the right balance in the technical rules between encouraging the development and use of new technologies in athletics and the preservation of the fundamental characteristics of the sport: accessibility, universality and fairness.” The IAAF also announced that it expected the working group “to report back by the end of the year.”

True to its word, on January 31, 2020, the IAAF promulgated new rules governing footwear. Among other things, the new rules stated that all racing shoes could have a sole no thicker than 40mm and contain no more than one carbon plate. In addition, in order to prevent athletes from racing in prototypes that might otherwise comply with the rules, “any shoe that is first introduced after [April 30,] 2020 may not be used in competition unless and until it has been available for purchase by any athlete on the open retail market (i.e. either in store or online) for at least four months prior to that competition.” Since the first day of Olympic track and field is, for now, scheduled to begin on July 31, 2020, and the Olympics marathons are scheduled to take place on August 8 and 9, any racing shoe used in the Olympics must, therefore, be released for sale to the general public by the end of April.

The IAAF president, Sebastian Coe, stated that:

As we enter the Olympic year, we don’t believe we can rule out shoes that have been generally available for a considerable period of time, but we can draw a line by prohibiting the use of shoes that go further than what is currently on the market while we investigate further.

True to Coe’s words, under the new rules, the Nike Vaporfly NEXT% is legal, as is its successor, the AlphaFly Next%, which was announced by Nike on February 5, 2020, less than a week after the new IAAF rules. The “stack height,” or “the amount of material between your foot and the ground” of the AlphaFly is 39.5mm, versus 37mm in the Vaporfly Next%. By way of comparison, the stack height of the Nike Zoon Streak 7, a conventional marathon racing flat, is 26mm. Thus, the Next% line features a sole that is approximately 50% thicker than its traditional counterparts. “Running twitter” has taken to referring to the Alphafly as #ChonkyBois.

Nike made a limited number of Alphaflys available to Nike Plus members on February 29, 2020, to coincide with the United States Olympic Marathon Trials. In a genius marketing coup, Nike made the Alphafly available, for free, to all athletes competing in the Olympic Marathon Trials. According to Runner’s World, about 25% of competitors opted to wear the Alphafly, even though those who are not sponsored by Nike had just received the shoes days before the race (you generally do not want to try new things during a marathon, like shoes or nutrition). Runners were willing to take this risk because, while the Vaporfly boosts performances by ~4%, the Alphafly may help twice as much.  The previously-unheralded Jacob Riley intentionally chose to forgo pursuing sponsorship until after the Olympic Trials so that he could race in the Alphafly. His gamble paid off, with a personal best and an Olympic berth.

Nike’s competitors are working to match the effectiveness of the Alphafly, but they’re not there yet. With its legality no longer in doubt, the Alphafly is here to stay, for better or for worse.