Imagine it’s Sunday, August 9, 2020, the final day of the Tokyo Olympics. The marathon has started, tens of thousands of people are lining the route, and the morning sun is radiating a furnace room of heat.

On August 9 this year (2017), the temperature hit a high of 37 degrees Celsius, or 98.6 degrees Fahrenheit. That’s hot man! And potentially dangerous for runners, as well as spectators. According to Makoto Yokohari, a professor of city planning at the University of Tokyo, in August the temperature at the location of the national stadium in Tokyo gets to 30 degrees at 7:30 am, and rises to the mid 30s in Asakusa, the mid-way point of the 2020 marathon. Yokohara adds in this article that much of the route, especially around the Imperial Palace, is not under shade.

Runner’s WorldFor runners, the fastest times often come in cool weather, in a range of 4.5 °C (40 °F) to about 13 °C (55°F), according to this analysis from Runner’s World. But when you run a marathon in hot weather, your body will rebel. According to this article from Scientific America, marathoners need blood to go in two directions at the same time – to your muscles to deliver oxygen and keep your muscles pumping, and to your skin so that your body can cool down. When it’s really hot, unfortunately, the blood that goes to the muscles that are getting a work out, gets even hotter, and the blood that gets to the surface doesn’t cool down. You sweat more, you dehydrate, and your body reacts with heat cramps, heat exhaustion, or even heatstroke.

The mother of all heat related illnesses. Your body temperature rises above 105 degrees F and it becomes a life-threatening situation. Most often, heatstroke results from untreated heat exhaustion, although it’s very possible for heatstroke to come about with no signs of heat exhaustion. Heatstroke is characterized by extreme fatigue and weakness, confusion and odd behavior, disorientation and finally unconsciousness. Your body’s regulatory system completely shuts down at this point, sweating ceases, and your skin becomes hot and dry. Unfortunately, it doesn’t end there. Convulsions and seizures can occur as your brain begins to shut down; coma and death are possible in the worst situations. GET OUT OF THE HEAT IMMEDIATELY! Seek medical attention, get in the shade, drink water, etc anything to get cooled down! You do NOT want to get to this point.

For us pedestrians, succumbing to the heat is commonplace in August, according to Akio Hoshi, a professor of health science at Toin University of Yokohama. “The number of people transported by ambulance due to heatstroke or heat exhaustion has peaked in early August in recent years. So the Tokyo Olympics fall in the period with the highest risk,” Hoshi said.

The 1964 Tokyo Olympics were held in October, and the weather was primarily wet and cold….preferable conditions to the marathoners of 2020.