Cold Weather Races Show How Climate Affects Running

The 2025 marathon in Boston was a shock to many. While the legendary 1976 race saw temperatures near 100°F and nearly half the runners quit, this year’s event started in the upper 30s to low 40s and climbed to about 50°F. Only a tiny fraction, 1. 5 percent of the 28, 854 starters, failed to finish. Humidity turns sweating into a problem: when it is high, sweat does not evaporate easily, so the body cannot cool itself. “Heat dissipation becomes an issue, ” said Thompson. In contrast, cold weather forces runners to focus on staying hydrated and keeping electrolytes balanced; skipping water can lead to cramps or even hypothermia. Coaches like Bob Rothenberg advise that the right clothing is more important than the weather itself. “There are no bad choices in weather, just bad choices in clothing, ” he says. Runners who train in winter learn which layers keep them warm without overheating, while those preparing for hot races focus on breathable fabrics.Nutrition also plays a key role. Adequate glycogen stores are essential for generating body heat, especially in cooler temperatures. If a runner runs out of glycogen, they lose the ability to shiver and stay warm, increasing the risk of hypothermia. At the same time, too much fluid intake without electrolytes can dilute blood sodium and cause hyponatremia. Recent research from a Brown University biostatistician examined 216 U. S. marathons in 2023 and found that performance drops when temperatures rise above about 53°F, with women and older runners showing greater sensitivity. Elite athletes, who train more rigorously for temperature extremes, are less affected by heat. The marathon also serves as a living laboratory for studying heat‑related illnesses, cardiac stress, and even “runner’s kidney. ”Students and researchers gather data each year to improve medical care for athletes, turning a competitive event into a source of scientific insight.