Taylor Knibb, a graduate of Sidwell Friends shown here competing at an event this year in Canada, placed 16th Wednesday at an Olympic women’s triathlon qualifying event in Tokyo with a time of 1 hour, 43 minutes and :07 seconds. (Jason Franson/AP)

With fears of extreme heat posing risks to athletes’ health, the final leg of the Tokyo Olympic qualifying event for women’s triathlon was pared from a 10-kilometer run to 5K just hours before Thursday’s 7:30 a.m. start at Odaiba Marine Park.

Though the American contingent was strong and deep, boasting five of the world’s top 20-ranked triathletes among the starting field of 65, none finished on the podium and only one, fifth-place finisher Summer Rappaport of Thornton, Colo., clinched a spot for the Tokyo Games with her performance.

Under USA Triathlon’s Olympic qualifying rules, as many as two spots were at stake for American women in the competition. But one would have had to finish on the podium in order for the second spot to be available. The U.S. is expected to send three female triathletes to the Tokyo Games, and there will be other opportunities to qualify next spring.

Rappaport’s time in the event — which consisted of a 1500-meter swim in a man-made lake, a 40-kilometer bike and the 5K run — was one hour, 41 minutes and 55 seconds.

Bermuda’s Flora Duffy won the event in 1:40.19.

The other Americans finished as follows: Taylor Spivey (Redondo Beach, Calif.) was eighth (1.41:38); Kirsten Kaspar (Scottsdale, Ariz.), was 14th (1.42.40); and Washington’s Taylor Knibb, a rising senior at Cornell, was 16th (1.43:07). The 21-year-old Knibb, a graduate of Sidwell Friends, was the youngest among the U.S. women’s triathlon delegation in the event and the current under-23 World Champion. It was a disappointing day for Katie Zaferes of Santa Cruz, Calif., the current world No. 1 and a 2016 U.S. Olympian. Zaferes was involved in a crash on the bike and withdrew.

Concern about Tokyo’s sweltering late-summer heat and humidity is a growing issue for several sports heading into the 2020 Olympics. That’s largely why the start of women’s triathlon test event was 7:30 a.m. Even then, officials with the International Triathlon Union chose to cut the running segment in half just four hours before the start, with the weather forecast indicating that conditions would fall within “extreme levels” by 9 a.m. local time, when the run segment was expected to begin.

The water temperature at the start of the event was reportedly 86.5 degrees; the air temperature, 89 degrees and the humidity, 66.4 percent.