# Why Your Usual Running Pace Feels Harder in the Heat—and What to Do About It
Heat and humidity transform easy runs into grueling efforts. Your body works harder because sweat becomes less effective at cooling you down in humid conditions, forcing your cardiovascular system to work overtime just to maintain the same pace.
Research from exercise physiology shows core temperature rises faster in hot, humid environments. Your heart must pump more blood to the skin for heat dissipation, leaving less oxygen-rich blood for working muscles. This explains why a 10-minute mile feels anaerobic on a 85-degree day.
Thermoregulation demands increase substantially. Studies published in the Journal of Applied Physiology confirm that heat exposure raises perceived exertion by 10 to 15 percent at identical workout intensities. Your body isn't weaker. The environment simply demands more.
Practical adjustments work. Slow down. Running 30 to 60 seconds per mile slower in heat prevents excessive core temperature elevation and reduces injury risk. This isn't weakness—it's physiology. Elite runners like Eliud Kipchoge adjust paces in hot conditions during training.
Hydration timing matters more than volume. Drink 400 to 800 milliliters of fluid two to three hours before running, then 150 to 250 milliliters every 15 to 20 minutes during effort. Sports drinks containing 6 to 8 percent carbohydrates improve performance in heat compared to water alone.
Heat acclimatization develops over 10 to 14 days. Training in warm conditions triggers your body to sweat earlier and more efficiently, reducing core temperature rise. Start with shorter efforts in cooler parts of the day, then gradually increase duration and heat exposure.
Schedule long runs early morning or late evening when temperatures drop.