Running in the Heat: Safety Guide for Runners
Heat stress diverts blood from muscles to skin for cooling, dehydrates the athlete, thickens blood, increases heart workload, and can cause cramping or fatal cardiac events. Practical strategies include temperature-adjusted pacing, early/late running, hydration, cooling tactics, and always having a backup plan.
How Heat Stresses a Runner’s Body
Running in heat is dangerous. When temperatures rise, the body’s physiology changes dramatically.
Heart
When temperatures rise, we sweat more. Sweating diverts blood from muscles and vital organs to the skin’s surface to release sweat. Two bad things happen:
- Rapid dehydration: We lose blood volume quickly.
- Increased organ stress: Muscles and vital organs work under greater stress load.
Specifically, hearts are under extreme stress. The heart must move blood around the body to fuel muscles. When losing blood volume through profuse sweating, the heart must work faster to meet runner demands. Heart rate increases; a normal run feels incredibly difficult.
Making matters worse, blood viscosity changes as we lose plasma. Thicker blood stresses the entire vascular system. Even a small heart anomaly can become fatal.
Muscles
Blood is diverted away from working muscles. Efficiency is compromised. Muscles must find other energy sources, and a long run quickly becomes an interval workout. This leads to cramping, often affecting the largest muscle groups first.
10 Tips for Running in the Heat
Adjust your pace to account for temperature. Use a temperature calculator to adjust expected times. A 65°F run at 7:00 pace might require 7:11 pace at 85°F.
Start slower than normal and increase pace if everything feels alright. Run a course allowing you to stop early. Running loops lets you stop at home for a drink every few miles on hot days.
Hydrate well before, during, and after your run. Drink plenty of water before (not all at once), consider diluted sports drink during to replace electrolytes, recovery drink after. Avoid drinking too much during hot weather.
Pee test: If hydrating well, urine should be lemonade-colored. Not clear, not dark. Dark yellow to brown spells trouble.
Run early or late. Summer long runs usually start around 5 AM. Things heat up quickly after 7 AM. Night running is popular but ensure you’re safe.
Look for shade. Run under trees to avoid direct sun. Concrete and pavement radiate heat, so prefer grassy areas or trails.
Stick your shirt in the freezer. Pre-cooling helps you stay cool longer. Your shirt can be damp but not soaking wet.
Put ice in your hat. A handful of ice cubes in your hat helps maintain coolness as long as possible.
Wear sunglasses. They protect eyes and keep your face relaxed, improving running form. They also deflect flying insects.
Use sunscreen liberally. Protect your skin from UV damage.
Have a backup plan. Carry a phone or tell someone your running route and expected return time. On hot days, consider having a friend available for pickup if you need it.
Related Concepts
Summer Races and Heat Stroke, Running in the Heat, Coaching High School Distance Runners
Bottom Line
Be safe and enjoy the miles this summer. Respect the heat. It’s not your enemy to conquer—it’s a force to respect and prepare for.