Going for your usual run or bike ride in hot temperatures can bring scary health hazards if you aren't adequately prepared. Heat can place strain on the cardiovascular system and cause serious illnesses such as dehydration, heat cramps, heat exhaustion, or heat stroke. Heat exhaustion, when someone's body temperature skyrockets to 104 degrees or higher, can develop from enduring many days of extreme temperatures and failing to properly rehydrate. If untreated, heat exhaustion can lead to heat stroke, a life-threatening condition that occurs when the body stops sweating and is unable to cool itself, according to the Centers for Disease Control and Prevention.
Sweating is a main way that the body cools itself; it's the result of water being brought to the surface of the skin through sweat glands, says Michael Bergeron, a professor in the department of pediatrics at the University of South Dakota's Sanford School of Medicine. We only begin to cool down once sweat evaporates; when it has trouble evaporating, such as in humid weather, our risk for overheating goes up, he explains. Signs of heat illness include nausea, cramps, headache, dizziness, lack of appetite, fatigue, and dark or amber urine, which signals dehydration.
Exercising indoors to stay cool may not always be an option. But you can still get in a good workout on warm-weather days by taking these precautions:
Acclimatize at low intensity
Adjust your workout when the heat wave hits. "The biggest mistake people make is that they don't work up to the heat and acclimate. It takes about one to two weeks to acclimatize to perform the best in the heat," says Samantha Clayton, a personal trainer and track coach based in Malibu, Calif. Clayton, who competed as a sprinter in the 2000 Olympic Games. She says that Olympic athletes arrive early at their events to acclimate to local temperatures.
To prepare for and adapt to hot weather, begin with shorter distances at an easy effort, says Robbie Ventura, former professional cyclist on the U.S. Postal Service cycling team. Next, lengthen the easy workouts and, after about four or five rides (or runs), you can increase intensity. As you adapt, your body will hold more moisture and become more effective at cooling itself.
Don't wait until you're thirsty to hydrate. Two hours before heading out the door, down 16 ounces of an electrolyte-fueled drink such as Gatorade, Clayton says. Drink another 6 to 8 ounces of water 10 to 15 minutes into your workout (yes, you should always run with water), he says. Even if you exercise briefly, replace fluids early in your workout.
Drinking electrolytes, found in sports drinks, will replace sodium and potassium that are lost when sweating. If you are low on electrolytes, you may experience heart palpitations, nausea, and headaches.
Evidence shows that even a 1 to 2 percent loss in body weight from fluid loss can boost your core temperature, putting you in the danger zone for dehydration. Weigh yourself before and after exercising to determine any amount of weight loss, and then drink 16 to 24 ounces of a sports drink to replace fluids for every pound lost. (Take note: This is not a safe way to lose weight!)
Keep cool even before you hit the pavement. Olympic athletes will take a cold shower, cool off in an air-conditioned room, or even sit in an ice bath before exercising in the heat, Bergeron says. Eating crushed ice before a long workout will help delay a rise in body temperature as well, he adds.
To stay cool during long rides and hill climbs, Tour de France cyclists put ice cubes in a sock, which they place on their backs, says Ventura, who spoke to U.S. News from France, where he was attending the race. To wick away moisture, the cyclists also wear light-color jerseys and unzip them to allow for ideal circulation.
Rise and shine early
Be like an Olympian, and get an early start. Pre-dawn runs or bike rides can help you beat the heat, and you'll benefit from better air quality before the mercury rises. "You need quality oxygen to help cool you down, so take a nice deep breath before you exercise," Clayton says. "Then your blood can do its work and get to the surface of your skin to cool you down."