Organizers of the 2020 Summer Olympics are heeding warnings from Japan’s Medical Association about Tokyo’s summertime heat and humidity, on Tuesday announcing that the marathon will begin at 6 a.m. local time (5 p.m. Eastern).

Racewalking, triathlon and rugby sevens also will take place in the early morning, while the mountain-biking events will start in the late afternoon to avoid the midday heat.

In October, Japan’s Medical Association expressed “grave concerns” about the risks for 2020 Olympic athletes and spectators, considering that temperatures in Tokyo usually top out in the mid-80s in late July and early August, with high humidity. Last summer was especially brutal, as a summer heat wave killed at least 138 people in Japan, sent more than 70,000 people to hospitals and was declared a national emergency. Temperatures in Tokyo reached 104 degrees Fahrenheit with 80 percent humidity.

“The Tokyo marathon normally gets [a half-million] to 1 million spectators. Even if 0.1 percent of them get ill from heat, that would amount to 500 to 1,000 people,” Makoto Yokohari, a professor of urban engineering at the University of Tokyo, told The Post in December. “Tokyo currently does not have the capability to rescue that many people, though starting at 6 may mean fewer spectators.”

Tokyo Olympic organizers are taking some steps to combat the heat, coating the marathon course and other major roads with more than 60 miles of a resin-based surface that reflects infrared rays and lowers the surface temperature by as much as 14 degrees Fahrenheit. Fans will be able to retreat to tents and stand under fans that emit cooling mist, though a plan to air-condition the new national stadium in Tokyo was abandoned because of the costs involved.

For comparison’s sake, the marathon at the 2016 Rio Olympics started at 9:30 a.m. local time and the temperature was around 66 degrees. A more apt comparison might be the 1996 Games in Atlanta, when the marathon started at 7 a.m. Temperatures that day reached 91 degrees, a few degrees above normal.

Next year’s Olympics will be held from July 22 to Aug. 9. In 1964, when Tokyo previously hosted the Games, they were held in October, but IOC officials are loath to move the Summer Olympics to the fall because of television conflicts with NFL football and the MLB playoffs in the United States along with professional soccer elsewhere around the globe.

“The Summer Olympics are simply of less value if held in October because of preexisting program commitments for sports,” Neal Pilson, the former president of CBS Sports, told Reuters last July.

Temperatures soared to 100 degrees in Atlanta during the first weekend of events in 1996, and similar temperatures were recorded in Athens eight years later.

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