Keep your cool while exercising in the heat.

Women's running legs, pink-gray sports shoe detail The dog days of summer are great if you’re lounging poolside with a magazine, but can present a challenge if you’re trying to maintain your fitness routine. Of course, it’s always more fun to exercise outdoors in the sunshine—just beware extreme heat and humidity, which can be downright dangerous when combined with intense exercise.

Heat and Exercise

Your body comes equipped with its own cooling system—the ability to sweat. When the sweat evaporates from your skin, it serves to cool you down. This cooling process can be compromised in hot, humid conditions. Exercising in hot weather places extra stress on the body. Both the hot temperatures and the exercise increase your core body temperature. As your body heats up, a variety of things happen:

  • Fluid loss: On a hot day, your body will lose double the amount of water it would lose on normal day.
  • Increased internal temperature: The external heat, exertion, and fluid loss cause your internal temperature to rise.
  • Decreased sweating: Humid air does not allow the sweat to evaporate from your skin and cool you off, so your internal temperature rises even higher.
  • Increased circulation and heart rate: The sweating and dehydration increases your heart rate, which can rise three-to-five beats per minute for every one percent of water loss you experience.

The bottom line: on a hot, humid day, you’ll feel like you’re working out much harder than you actually are. What’s more—you run the risk of experiencing heat-related illness. Recognizing Signs of Heat-Related Illness If you plan to exercise in the heat and/or humidity, it’s important to recognize the signs of heat-related illness.

  • Heat cramps: Heat cramps are painful muscle contractions, typically affecting the calves, quadriceps, and abdominals. With heat cramps, your body temperature may be normal, but the affected muscles can feel firm to the touch.
  • Heat exhaustion: During heat exhaustion, the body temperature rises as high as 104 degrees Fahrenheit and you may experience nausea, vomiting, fainting, headache, weakness, and cold, clammy skin. Left untreated, heat exhaustion can lead to heatstroke.
  • Heatstroke: Heatstroke is a life-threatening, emergency condition. During heatstroke, the body temperature rises higher than 104 degrees Fahrenheit and although your skin may be hot, your body will likely stop sweating. Heatstroke is often accompanied by confusion and irritability. Heatstroke requires immediate medical attention to prevent brain damage, organ failure, or death.

When exercising in hot conditions, watch for the signs and symptoms of heat-related illness such as muscle cramps, nausea, dizziness, confusion, or headache. If you develop any of these symptoms, stop exercising immediately, lower your body temperature, and get hydrated. If you don’t feel better within 30 minutes, seek medical attention. Exercising Safely in the Heat The best way to “treat” heat-related illness is to prevent it from occurring in the first place. This doesn’t mean you have to forego your summer exercise program; it just means you need to exercise common sense and take some safety precautions. Follow these guidelines for a summer full of safe exercise:

  • Acclimate: As the temperature rises, give your body time to adjust to exercising in the heat. Gradually increase the duration and intensity of your workouts, allowing one to two weeks to adapt.
  • Weigh yourself: Weigh yourself before and after exercise. This will help you monitor your fluid loss and match your fluid intake accordingly. You lose about 2.5 cups of water per every pound of body weight lost.
  • Stay hydrated: It’s imperative to stay hydrated. Dehydration is one of the biggest contributors to heat-related illness. For optimal hydration, drink 20 ounces of water two hours before you plan to exercise and then 8 ounces of water immediately before heading out. During exercise, take a drink every 15 minutes, even if you are not thirsty, as thirst is not a good indicator of hydration. Water is generally best, but if you plan to exercise for more than an hour, a sports drink or electrolyte replacement may be necessary. After exercise, replenish accordingly—and drink beyond thirst.
  • Slow down: The heat will already add to your exertion levels, so this is no time for intervals or world records. Adjust your pace to accommodate the added intensity from the heat.
  • Time it right: During the dog days of summer, early mornings or late evenings are best. Head out as early as possible to catch the coolest part of the day or wait until after dinner. Avoid the midday heat.
  • Dress appropriately: Wear light, breathable, wicking clothing that will help the sweat to evaporate. Avoid cotton, which will become damp and trap the sweat next to your skin rather than allowing it to evaporate.
  • Shade: Seek shade whenever possible. Avoid areas with full sun exposure, as this will only add to the intensity of the heat.
  • Sunscreen: Sunscreen is always important, but especially when exercising in the heat. A sunburn interferes with the body’s ability to cool itself.
  • Know when to say no: Sometimes it’s simply too hot or humid to exercise outdoors safely. As a general rule, if the temperature is 90 degrees Fahrenheit or higher and the humidity level is 60 percent or higher, take your workout inside, or opt for swimming laps in the pool.
  • Listen to your body: A variety of factors can increase your sensitivity to the heat, including fatigue and illness. Assess the signs and symptoms of your own body—not your exercise partner’s body—to decide whether it’s a good day to exercise in the heat. If you exercised hard yesterday, today might be the time to take it easy.
  • Pay attention: Pay attention to the signs and symptoms of heat-related illness and take immediate action.