The proposal comes weeks after marathons were run around midnight in 38 degrees C (100 degrees F) at the track and field world championships in Doha, Qatar. Forecast temperatures in Sapporo are "five to six degrees centigrade cooler during the day than in Tokyo," the Olympic body said.
"The Olympic Games are the platform where athletes can give 'once-in-a-lifetime' performances, and these measures ensure they have the conditions to give their best," IOC President Thomas Bach said in a statement.
Still, one Olympic medal contender affected by the plan questioned if athletes were consulted. "I'm assuming this means you'll be paying for my family and friends flights and accommodations who have already booked for Tokyo?" Evan Dunfee of Canada, who took worlds bronze in the 50-kilometer walk, wrote in a Twitter post tagged to the IOC and track and field's world body.
"This breaks my heart and is poised to ruin my Olympic experience. Was there ANY consultation with athletes over this?" Dunfee wrote. An Olympic panel has been consulting with sports governing bodies while assessing heat and weather issues for the July 24-Aug. 9 Tokyo Games.
"The IOC working group identified the marathon and race walk as the events that would put particular heat stress on the athletes," it said. The marathons were already due to start at 6 a.m. in Tokyo to ease the heat effect on runners. The men's 50-kilometer race walk final was slated for a 5:30 a.m. start.
The IOC said it informed the governing body of track will also consult Olympic teams and broadcasters. "Giving athletes the best platform for their performances within the environment they are in is central to all major events," IAAF president Sebastian Coe said in the IOC statement.
In Doha, 28 of 68 starters failed to finish the women's marathon and 18 of 73 men failed to complete the course. Ethiopian distance-running great Haile Gebrselassie said athletes "could have died" in the women's race.
An Olympic panel overseeing preparations will discuss heat measures at its Oct. 30-Nov. 1 meeting in Tokyo. "These include better shade, water sprays, better access to water supplies and an initiative to help the athletes in their preparations," the IOC said.
The plan driven by increasing summer heat cuts into a key promise of Tokyo's bidding, first for the 2016 Olympics won by Rio de Janeiro and then its successful 2020 campaign, to deliver a "compact games" with 85% of venues in an 8-kilometer (5-mile) city center cluster.
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