Distance running performance tends to be best in cool conditions; the cold mainly slows the first minutes through cooler muscles and raises local risks to exposed or wet skin
Interpretation
Large observational race datasets agree that cool beats warm: men in seven North American marathons were 1.7% slower than course records at WBGT 5-10 °C vs 4.5% at 20-25 °C (Ely 2007); 1,791,972 marathon performances showed optimal temperatures of about 3.8-9.9 °C by ability (El Helou 2012); 7,867 elite athletes in 1,258 races ran best at WBGT 7.5-15 °C, losing 0.3-0.4% per °C outside it (Mantzios 2022). A small lab study (8 men, cycling) found the longest endurance at 10.5 °C (Galloway 1997). Muscle performance changes about 2-5% per 1 °C muscle temperature (Racinais 2010), explaining slow early kilometres, but aerobic performance in real cold is under-studied (Castellani 2015). Gaps: observational designs, mostly trained or elite runners and men in lab work, no triathletes, little data on very cold conditions.
Practical implication
Treat cool weather as good running weather; warm up gradually, keep warm between efforts, dress for the middle of the run, and protect hands, ears, face and wet skin, with extra caution for wind, rain and long slow sessions. People with asthma or heart disease should follow a medical plan. Extrapolated from race data and small lab studies, not triathlete trials.
Sources
8 sources, independently verified.
Race days grouped into WBGT bands of 5-10, 10-15, 15-20 and 20-25 °C. Men were 1.7%, 2.5%, 3.3% and 4.5% slower than course records across the bands (significant); women 3.2% to 5.4% (not significant). Performance slowed progressively from 5 to 25 °C WBGT, and slower runners were more affected. Conditions below 5 °C WBGT were not studied. Observational race data.
Optimal temperature for maximal mean speed varied by performance level from about 3.8 to 9.9 °C. Above these optima running speed fell and withdrawal rates rose; Chicago 2007 at 25 °C had the highest withdrawal rate (30.74%). Observational; cannot separate temperature from other race-day factors.
Race-day WBGT ranged from -7 to 33 °C; 27% of races were cold or cool. Optimal WBGT was 7.5-15 °C (about 10-17.5 °C air temperature), and performance fell about 0.3-0.4% per °C WBGT outside that range. Air temperature was the most important weather factor. Elite athletes only.
Cycling to exhaustion at about 70% VO2max at 3.6, 10.5, 20.6 and 30.5 °C. Time to exhaustion was longest at 10.5 °C (93.5 min) and shortest at 30.5 °C (51.6 min); temperature had a significant effect. Small, all-male, cycling rather than running, low airflow.
Review: short-duration performance improves by about 2-5% per 1 °C rise in muscle temperature; performance impairments in cold and hot environments are linked to changes in neural drive and neuromuscular transmission. Mostly short, powerful efforts rather than endurance running.
Review: aerobic performance in the cold has not been thoroughly studied, with only a few studies suggesting it is degraded (lower deep body and muscle temperature, cardiovascular changes, altered metabolism). Strength and power fall during cold exposure mainly via muscle cooling. Cold tolerance varies with habituation, anthropometry, sex and fitness.
Exercise can be performed safely in most cold-weather environments. Recommends knowing the signs and risk factors for hypothermia, frostbite and nonfreezing injuries, individually chosen clothing, using the wind-chill index to estimate frostbite risk with heightened surveillance below a wind chill of -27 °C (-18 °F), and closer monitoring of people with asthma or cardiovascular disease.
32 high-quality studies (mean PEDro score 7.6 of 10): warming up improved performance in 79% of the criteria examined. Not specific to cold conditions; mostly short, intense tasks.