Running in Hot Weather: 8 Tips to Stay Safe and Perform

Summer heat doesn't have to stop you from running. With the right preparation and adjustments, you can continue training safely while your body adapts to warmer conditions. Understanding why heat affects your performance helps you make smarter decisions that protect your health and support your long-term goals.

Why running in the heat is more demanding on your body

When you run in the heat, your body works harder to cool itself down through thermoregulation. This process diverts blood flow from your working muscles to your skin to release heat through sweat. Less oxygenated blood reaches your muscles, causing your heart rate to increase and your pace to naturally slow.

Humidity makes this challenge worse. The heat index— combining temperature and humidity — is a better guide than temperature alone. When humidity is 70%, a 90-degree day can feel like 105 degrees, preventing sweat from evaporating and increasing overheating risk.

How to prepare for your run

Acclimate to the heat

Acclimating to 130 degree temperatures was vital to Will Goodge during the Marathon des Sables, the 7-day ultra marathon across the Sahara Desert.

It can take one to two weeks to acclimate to hot weather. Spend an hour or two outdoors daily when you plan to work out, avoiding long or high-intensity sessions during peak heat. Running in the heat without proper acclimation can be dangerous.

Heat exhaustion and heat stroke result from your body overheating. Pushing to the point of heat exhaustion will hurt rather than help your heat tolerance according to the CDC.

Prehydrate, carry water, and rehydrate

You can lose up to 12 ounces (350 ml) of fluid and electrolytes in 20 minutes while running in hot weather. When dehydrated, your blood volume decreases, reducing blood flow to your skin and muscles. This can increase your heart rate and impact cognitive function.

Drink 2 cups (500 ml) of water two hours before your run and 6 to 8 ounces 15 minutes before starting. Carry water if your run lasts more than an hour. Rehydrate afterward to replace fluid deficits and boost recovery.

An analysis of WHOOP data shows that proper hydration is one of the best things our members do to improve their daily recovery.

Dress for the weather

Wear comfortable, loose-fitting, and light-colored clothing made from breathable fabric in hot weather.

Loose tops and shorts help your body breathe and cool itself. Dark colors absorb heat while tight clothing restricts cooling.

Choose synthetic fabrics that wick away perspiration and dry quickly. Clothing with vents or mesh provides additional cooling.

Protect your skin

The sun's ultraviolet rays are at their strongest between 10 am and 4 pm. Avoid direct sunlight during those hours or take protective measures. Wear a light-colored hat, sunglasses, and sunblock with at least SPF 30.

How to adjust your run in the heat

Run in the early morning or late evening

Avoid the heat of the day by running early or in the evening. If you must run at midday, choose a shaded route. Morning runs help you avoid peak heat and your muscles are usually looser than in the mornings and you’re less likely to injure yourself.

Slow your pace and manage your effort

For most runners, perceived exertion increases when temperatures rise above 59 degrees (15 degrees Celsius). Research shows that faster runners slow approximately 1 second per mile for every 1 degree Celsius above 15 degrees. Slower runners (7:25 to 10-minute pace) slow 4-4.5 seconds per mile per degree.

Male runners are more affected by high heat than female runners. Adjust your pace if your heart rate is too high or your effort becomes uncomfortable.

Know the signs of heat exhaustion and heat stroke

Heat exhaustion and heat stroke are serious medical conditions that happen when you are overheated, dehydrated, or dressed too warmly. Below is a chart of the differences between heat exhaustion and the more serious heat stroke.

Signs of heat exhaustion and heat stroke, and what to do in each situation.

The performance benefits of heat acclimation

Training in the heat leads to powerful physiological adaptations. Your body becomes more efficient at cooling itself, sweating earlier and increasing plasma volume. Your heart pumps more blood with each beat, and your heart rate decreases for a given pace.

These adaptations improve performance in both hot and cool conditions. Studies show that training in hot weather can increase cardiovascular fitness, build resilience, and improve rate of perceived exertion.

Use data to guide your run

Wearing a heart rate monitor like WHOOP helps you track your HR and avoid overexertion in hot weather. WHOOP provides live heart rate and daily Strain recommendations. It shows your Strain building in real time, helping you decide whether to push harder or rest in the shade.

See your live heart rate during your workout with WHOOP.

Train smarter, not just harder, in the heat

Running in the heat requires balancing adaptation with respecting your body's limits. Prepare properly, adjust your effort, and listen to your body's signals. Understanding your personal data helps you navigate this balance.

When you see how your body responds in real time, you make smarter decisions for immediate safety and long-term performance. Ready to see how your body adapts? Join WHOOP.

Frequently asked questions about running in hot weather

What temperature is too hot to run in?

No single temperature is too hot for everyone — it depends on humidity, sun exposure, and personal acclimation. Use extreme caution when the heat index approaches 90°F (32°C). When the heat index exceeds 100°F (38°C), the risk of heat-related illness is significantly higher.

Is it okay to run in 90-degree weather?

Well-acclimated and hydrated runners can run safely in 90°F (32°C) weather with significant adjustments. Slow your pace, shorten your distance, run during cooler parts of the day, and watch for overheating signs. If you're not heat-acclimated, avoid running in these conditions.

How long does it take to acclimate to heat?

Full heat acclimation takes 10 to 14 days of consistent, progressive exposure. Start with shorter, less intense workouts in the heat and gradually increase duration and intensity. Your body will adapt by improving its ability to sweat and regulate core temperature.