A recent study revealed that marathon race temperature is the single, most important factor in determining race performance. And, this isn't just for elite athletes either. The study, which took place over a 10-year period, analyzed approximately 1.8 million marathon participants in 6 major European and American marathons (Berlin, Paris, London, Chicago, Boston, New York). The study found that the significant impact of air temperature was true for runners of all levels as well as both genders. It further found that any increase or decrease in temperature from optimal temperature resulted in altered performances.

Warm Weather . The study found the significance of warm weather on runners to be the body's limited ability to thermoregulate. Incidences of hyperthermia were commonly reported. Hyperthermia is characterized by an internal body temperature of 39℃ (102.2F) or higher. Humidity was found to by a co-factor in performance as well. A greater number of DNR's were found in this category. Optimal temperatures to run in to get maximal results range from 3.8℃ - 9.9℃ (about 39F to 50F) with a loss in speed of 0.03% per every 1℃ in temperature increase. Bottom Line: Increasing temperatures above the optimal mean slower marathon times.

Cold Weather . The study revealed that the there is also a decline in pace with large dips in temperature below the optimal temperature range. In colder temperatures, the body requires more oxygen to maintain the body's baseline metabolic rate, which is responsible for regulating the body's core temperature. Additionally, in cold temps, the body relies more on carbohydrates for fuel than fat, which increases lactate production, causing a decline in performance.

Bottom Line: Large decreases below the optimal temperature mean slower marathon times.

Optimal Weather . As stated earlier, the optimal temperature for marathon running is between 3.8℃ and 9.9℃. Researches analyzed Haile Gebrselassie's 4 performances in Berlin and found that both of his World Records were achieved at the lowest temperatures (14℃ in 2007 and 13℃ in 2008, vs. 18℃ in 2009 and 22℃ in 2006 when he also won both races, but did not set world records). Within this temperature range, the body can perform at its optimal because internal temperature is more easily maintained.

For more information on this study, click here.