Marathon organizers can plan the course and distance, but the weather remains uncertain. Ted Metellus, event production director and race director for New York Road Runners, said heat is now a major focus of preparations, particularly after unusually warm conditions at the 2022 New York City Marathon. Temperatures at the Central Park finish were about 12 degrees Celsius higher than the previous year, and the average finish time was 11 minutes slower, according to Road Runners data. The organization responded by expanding its preparations, including making more misting stations available for deployment regardless of the temperature.
Research suggests the conditions linked with strong marathon performances differ by gender and ability. A 2012 study of nearly 1.8 million finishers across six major races found that the average ideal temperature for the fastest 1% of men was 4 degrees Celsius, compared with 10 degrees for the fastest women. Among recreational runners, the corresponding averages were closer: 6 degrees for men and 7 for women.
Chris Tyler, an environmental physiology professor at the University of Roehampton, said faster runners generate more heat because they exert themselves more intensely, making cooler conditions more favorable. Slower runners produce less internal heat and can tolerate somewhat higher temperatures. Mike Tipton, a professor at the University of Portsmouth, explained that in hot conditions the body sends more blood to the skin to release heat, leaving less available to supply working muscles. That can bring on fatigue sooner and force runners to slow down.
The risks can become severe when the body cannot keep up with the heat. In 1984, New York City Marathon temperatures reached 26 degrees Celsius, with humidity above 90%. Of the 16,315 people who started, 14,590 finished, and hundreds received treatment for heat-related problems, according to The New York Times. French runner Jacques Bussereau collapsed in Queens after about 22.5 kilometers and later died of cardiac arrest. Race founder and director Fred Lebow called it “the disaster of 1984.”
Chicago’s 2007 marathon was also stopped while underway as temperatures reached 31 degrees Celsius and the dew point stayed near 20 degrees for several hours. More than 300 people were taken from the course by ambulance, 49 were hospitalized, and a 35-year-old runner who collapsed around kilometer 29 later died. In response, Chicago introduced a unified command center involving emergency services and other agencies, added a meteorology expert to its team, and established a color-coded event alert system to communicate changing conditions. The system has since been adopted by other major races, including New York.
Some organizers have changed race dates as well as their preparations. The Twin Cities Marathon will move two weeks later, to the first Sunday in October, starting in 2027. The decision followed a review of weather data and conditions, after extreme heat led to the event’s first-ever cancellation in 2023. Temperatures in the Twin Cities reached 33 degrees Celsius that day, an October record.
Organizers also considered overnight temperatures, since the race starts early in the morning. Event operations director Ed Whetham said nighttime lows had been gradually rising over the previous 15 years. Twin Cities In Motion president Dean Orton said the race’s original aim was to take advantage of a cool autumn morning, but long-term weather trends increasingly made the event feel like a late-summer race. Moving it later is expected to lower average temperatures by about 5.5 degrees Celsius, Orton said.
When changing the date is not an option, runners can prepare for heat through acclimatization. Tyler said this helps the body adapt to exercise in warmer conditions. Tipton said exercising in the heat for about an hour and a half a day over 10 to 14 days can help, as the body increases its circulating blood volume and begins sweating earlier.
The need to prepare may grow as temperatures rise. A 2025 Climate Central analysis of 221 marathons worldwide estimated that by 2045, 190 races—86% of those studied—would be less likely to have race-day temperatures within the ideal range for at least one group of elite or recreational runners. New York City was among them: the analysis projected a 2-to-5-percentage-point decline in the likelihood of ideal temperatures for each of its four groups of male and female elite and recreational runners.
Sources: Folha Esporte.