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It's freakin' hot in the U.S. now unless you're under a blanket of marine air on the Pacific Northwest coast or snowboarding at 10,000 feet. Even the chamber of commerce has to admit it's no longer "pleasantly warm" at 90 in Miami or 118 in Phoenix.
Heat is not about just comfort, a bad hair day, or sweat in your eyes; it's often about life and death. 200-300 U.S. residents - as many as 1,700 in a really bad summer -- die from the heat and its directly related effects each year. It kills more people in the U.S. than all other natural disasters combined except frigid weather, triggers many fatal heart attacks, and makes millions miserable. Heat exhaustion is very serious, hyperthermia kills hundreds in heat waves, and heat stroke is a full-fledged 911 event requiring immediate extreme measures to save the victim's life.
For now let's bypass those morbid, urgent health emergencies and concentrate on ways to stay more comfortable, stay safe, and get on with daily life, including exercising safely. A few facts about how our bodies heat up and cool down will suggest several ways to stay cooler for general comfort and for exercising in the heat.
Your body keeps itself near 98.6 degrees even at rest in a cool room by burning calories. Activity accelerates that process by up to 2,500%, so our bodies must sometimes shed some serious excess heat. Our primary heat-shedding organ is our skin, so sweating helps if the humidity is low enough to evaporate it, a breeze helps if the air is cooler than our skin, and shade helps, period. Heavy breathing - no, not that, just heavy breathing; let's focus here - dissipates heat if the air is cooler than our bodies. High humidity, air hotter than our skin, layers of fat, exercise, lack of acclimatization to the heat, sunburn, and being too old, too inebriated, or too young to notice symptoms all impede the body's attempts to cool us down to 98.6.
Exercise precautions start as early as 70 degrees and 60% humidity, a Heat Index or Apparent Temperature of 76, where sweats or warm-up suits can overheat any of us and overweight people should back off because they dissipate heat more slowly. At 73 degrees, even lean runners should back off a bit, and overweight people should stick to slow jogging or just easy calisthenics. 75? Slow jogging even for athletes, and everyone should watch for discomfort or facial discoloration. At 78 jogging becomes risky; light calisthenics or swimming is safer. At 80 degrees, we should confine
continuous activity to water sports.
In support of those surprising numbers, consider that a review of hundreds of thousands of Marine Corps recruits found that exercise-related heat
casualties increased progressively as air temperatures rose above a Heat Index of about 65°F. The risk of exercise-related heat injuries on mild days skyrocketed if the preceding day had included exercise in very hot weather. There is clear evidence that the effects of heat stress are both dose-related and cumulative.
Heat disorders share one common feature: the individual has exposed himself to, or generated, too much heat for his age and physical condition. By 90 degrees on a humid day, the body is doing everything it can to cool down to 98.6 degrees even as it sits watching TV. The heart is pumping a torrent of blood through dilated vessels and the sweat glands are dumping water and electrolytes overboard. Exercise in those conditions can be life threatening. Heat disorder severity tends to increase with age; what produces heat cramps in a teenager may produce heat exhaustion in his dad and deadly heat stroke in his grandfather.
Countless people get by, although in misery, with ignoring heat-aversion advice, but hundreds of others die from ignoring it. Why incur certain misery, or risk a 911 call, unless one is training to compete for big bucks in the heat next week? It's not like exercise in the heat is fun, and there are many ways to exercise in greater comfort. After all, it's the amount of exercise, not the amount of discomfort, that determines the benefit of a workout. Less pain => greater gain.
People unwilling or unable to back off outdoor dry land activities need to protect their health. The best protection for the obsessed exerciser or the professional athlete or roofer is acclimatization to the heat, which requires at least two weeks of regular, careful daily exercise in continuous hot weather. The most significant adjustments include increased blood circulation and volume to deliver more fluids and oxygen and remove more waste and heat, plus earlier, greater, and less-salty sweating to improve cooling and control electrolyte balance. Evaporation of one hefty bead of sweat from our skin relieves the body of 580 calories of heat, dropping the temperature of a quart of blood by 1.8 degrees Fahrenheit.
These processes all involve fluids, which must be supplemented. Your body absorbs fluids better when you drink frequently and in small amounts rather than drinking large amounts at one time. It also helps with fluid absorption if you eat something -- even if only a pinch of sugar and salt -- while drinking. Diluted sports drinks work well for this purpose; caffeine (unless one is accustomed to drinking a lot of caffeine) and alcohol are counterproductive.
If working or playing in the heat is more important than your health, start acclimatizing slowly when the weather heats up in the spring. If possible, work or play in front of a fan. Exercise should be fun, or at least fairly comfortable -- certainly not dangerous. Getting overheated is counterproductive because it makes you shorten your work or play. Exercise-related heat stroke is the second most common form of death in athletes in the United States, and we weekend warriors should be even more careful than acclimatized athletes to quit the minute we experience dizziness, weakness, nausea, cramping, or vomiting. Machismo is a commonly fatal disease.
Of course, you could just quit exercising for a month or two. You'd lose almost no conditioning, so the greatest risk is losing the exercise habit.
Now that you're exercising more safely, let's consider some less urgent measures to cheat the heat. Who wants to go into a job interview all sweaty, be miserable, or even collapse at a picnic?
White vehicles and white, cotton, long-sleeved clothes make a huge difference in our comfort in sunny climates. A cool- wide-brimmed hat and louvers in your hatchback add dramatically to those benefits. Once that solar heat gets into your vehicle or your body, getting rid of it very significantly challenges its cooling system. Even if you think dark cars and dark, synthetic clothes look better, "being cool" has two meanings. Which one is more important to you?
Volleyball ... softball ... mowing the lawn ... jogging ... and heat. In moderate to dry humidity, wetting down your clothing makes a big difference in comfort. For ladies, a short-sleeved sweatshirt avoids the wet-T-shirt-contest look when hosing down.
Put less fuel on your inner fires. Proteins (e.g., cheeseburgers, pizza) increase both metabolic heat production and water loss ... a double whammy in the heat. That's one reason eating supper first thing in the cool, cool, cool of the morning is of benefit in the summer.
We've all seen people jogging at noon at 85 degrees, not training for a hot (i.e., dangerous) marathon next week but just trottin' along to burn up some calories. Uncomfortable, unhealthy, unwise, unnecessary, counterproductive.
Fans inside a room don't cool rooms; they cool only the people they're blowing directly on. They are especially effective in cooling us down as we work or play hard, so we can stay more comfortable, get more into and out of the activity, and reduce heat-related health problems.
The National Weather Service has devised a research-based Heat Index, aka the Apparent Temperature. It is an accurate measure of how hot it really feels when effects of the relative humidity are combined with the actual air temperature. It explains why the western U.S. climate feels so much cooler than the eastern U.S. climate. You think Phoenix is hot at 120 degrees? Try Miami at 86! The hottest temperature ever recorded in bone-dry Albuquerque, 107, is more comfortable than St. Louis or Dallas at 83 on a totally muggy day! It's not just the heat, folks ... it really IS the humidity!
Then there's the obvious solution to all those issues: go jump in the lake. Sweating in a swim suit beats sweating in a business suit, the water's right there to cool us off, and in the heat swimming beats jogging ALL to heck. Play all the volleyball or Frisbee or keep-away you want, but do it in the water.
Be cool, man. It's SO much more fun, productive, and healthy.
For much more detail on these and life-threatening heat factors, click on