Running in Hot Weather

The best defense against heat is hydration. Therefore, when the temperature goes up, so should your fluid intake. Water should always be your number one drink of choice. Drink before, during, and after you run. Drink before you go to sleep, and drink when you wake up. In short, drink water often throughout the day, regardless of weather conditions. In general, you should drink at least eight glasses of water a day. When it's really hot out, you can easily double this amount. However, be mindful not to drink excessive amounts of water; avoid hyponatremia.

Always drink before you run and try to drink about 8 ounces every 25–30 minutes while you run. Although just water is fine for runs of up to an hour, you will find that sports drinks maintain your performance level for runs over 1 hour. Most popular sport drinks have a low level of electrolytes and also contain carbohydrates (both simple and more complex polymers) to help speed up glycogen replacement.

Please don't count coffee, beer, or other caffeinated and alcoholic beverages as part of your daily tally of fluids. Although research has shown that caffeine does seem to enhance performance, depending on how long your run is, remember that a caffeine buzz can turn into a wilt. You may not want to skip coffee before you run, but just make sure you drink plenty of water, too.

Immediately following exercise, muscles are most receptive to absorbing carbohydrates (which later convert to the stored energy glycogen), which is why you'll often find bagels and fruit offered at the end of a race. But don't forget to meet your overall fluid replacement needs with water as well as with fluids containing ample carbohydrates, such as fruit or vegetable juices.


Perspiration and evaporation of perspiration are the primary means for the body to cool during exercise. Sweat glands become active as body-core temperature rises. One liter of sweat is generated during the expenditure of about 500 kilocalories (kcal). Skin blood flow also increases significantly during exercise. Blood flowing near the surface enhances cooling by both conduction and convection.

To help you stay hydrated during long, hot summers of running, consider stopping at every water fountain you pass and taking a drink. Don't forget to give yourself a minimum of two weeks to fully acclimate to the heat. The best way to do this is by running a slow 3–4 miles, making sure you have enough water. Gradually increase your distance and cumulative time running.

Also try combining indoor treadmill running with outside running to get more distance on really hot days. During the first hot, humid days of spring and summer, slowly build your mileage to acclimate to these conditions before considering running at a faster pace. In fact, many seasoned runners put their fast-paced efforts on hold until cooler weather returns. Additionally, try to miss the heat by running early in the morning or late at night. Remember, though, that if you run early in the morning, you may experience more humidity. And, of course, consider using an indoor treadmill on the worst days. That way you can get a workout with a few more miles in a cooler environment.

Heat-Induced Illness


Make sure you are aware of any medical conditions you have or of any medications you are taking that affect your tolerance for exercise in the heat. Medical conditions affecting heat tolerance include diabetes, high blood pressure, anorexia nervosa, bulimia, obesity, and fever.

Several illnesses can be induced by heat. The first, heat exhaustion, is caused by dehydration. The symptoms include chills, lightheadedness, dizziness, headache, and nausea. Body temperature usually rises to between 100–102 degrees Fahrenheit, and profuse sweating is evident. To treat heat exhaustion, move to a cool, shaded area, call an ambulance, and drink fluids until help arrives.

Heat stroke, a serious heat-induced illness, is caused by a sudden failure of the body's thermoregulatory system. Not only is this dangerous, but it can also be fatal. Heat stroke initially presents like heat exhaustion but can rapidly progress to more serious neurological symptoms, such as disorientation, loss of consciousness, and seizures. Body temperature can rise higher than 104 degrees Fahrenheit. Sweating is often absent, but the skin can be quite moist from earlier perspiration. The pulse of a person afflicted with heat stroke is usually more than 160 beats per minute, and blood pressure may be low.

If you are suffering from heat stroke, your core temperature must be reduced immediately. Kidney damage (acute nephropathy) occurs in about 35 percent of cases. This is a result of rhabdomyolysis (muscle breakdown) and myoglobinuria (excretion of muscle breakdown products in the urine), which contribute to kidney injury. Liver damage is also evident when liver enzymes are measured following heat stroke. Oftentimes getting packed in ice reduces core temperature. Heat stroke is a medical emergency. It is vital that you seek immediate medical attention.


If you run when it's dark (at any time of the year), wear a reflective garment. Reflective garments are made of high-tech materials that provide safety, comfort, and temperature control to keep you cool in the summer and warm in the winter.

Avoiding Heat Stress Injury

To avoid heat exhaustion or heat stroke, drink plenty of fluids (preferably water) 25–30 minutes before exercise and then 8 ounces every 25–30 minutes while exercising. After exercising, drink more fluids than you think you need, especially if you are over the age of 40. Don't wait until you feel thirsty; by that time you're already dehydrated. Drinking fluids while you exercise as well as when you're finished helps speed your recovery.

You can also protect yourself from the heat by gradually building up your tolerance for running in warmer weather. Stay fit, and don't overestimate your level of fitness. Individuals with a higher VO2 max (the amount of oxygen delivered to your muscles every minute) are more tolerant of heat than those with a lower VO2 max.


It is important to remember that environmental comfort is a highly individualized matter. By experimenting with a variety of layering apparel, you can learn how to dress effectively and comfortably for facing the elements. This in turn will enable you to train both safely and consistently.

Dressing Cool for the Heat

Even if you feel like you don't want to wear anything at all when it's really hot out, don't make that mistake! The worst thing to do is to overheat your body and then, with no protection, expose it to rapid cooling. This can cause lightheadedness and dizziness or a more serious heat injury.

When running in the heat, wear lightweight fabrics that wick away moisture, support your body, and neutralize odor. There are all sorts of comfortable and fashionable shorts and tops available for men and women. Workout apparel these days is about comfort, fit, performance, and style.

As for upper body wear, women can opt for a colorful sports bra and men a breezy fabric singlet. Thin, absorbent socks can keep your feet from getting too sweaty and minimize blisters. To keep sweat from dripping into your eyes, you might want to wear a headband or a visor. Even though baseball caps shield the sun, they trap heat—something to consider on hot, humid days. Don't forget to apply heavy-duty sunscreen, especially on your face.

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