Olympic events were shifted around on Thursday, as athletes struggled to compete in Tokyo's summer heat.
Ollie Jay is a professor of health and heat at Sydney University in Australia.
He says the real threat to Olympians - is actually Tokyo's humidity.
“The humidity is the climate that is really restricting the capacity to lose heat in this particular case. So, you might be able to produce lots and lots of sweat, but if that sweat can't evaporate from the skin, then it doesn't contribute to body cooling and that becomes really problematic.”
Jay suggests to cool down, competitors should try using electric fans and wrapping ice towels around to head, but don't touch your sweat.
"It's not the production of sweat that cools you down, it's the evaporation of sweat. So, as you're wiping yourself down, you're removing the sweat that you've secreted. You're progressively dehydrating the body for that sweat is not evaporating and providing any cooling to the body whatsoever."
Temperatures during the Games have regularly hit or exceeded 90 degrees Fahrenheit.
The International Tennis Federation shifted their Thursday morning matches to late afternoon, hoping shade would protect the players.
During his third round match on Wednesday, Russian tennis player Daniil Medvedev took a medical time out and called the trainer onto the court twice.
It was a stifling 99 degrees.
He told the umpire, “I can finish the match, but I can die.”