day 10: will the heat EVER go away?

I received a handful of suggestions in response to my post yesterday about coping with heat. In response to one reader's comment, I added wearing long sleeves to #2 about protecting your skin and #4 about staying cool. So long as you wear an appropriate, breathable, and light fabric, long sleeves can actually help keep you cool by reducing the surface area of your skin that is exposed to the sun.

One reader heard something on the local NPR station this morning about heat acclimation, and I decided to do some research on it all and this is an amalgamation of what I came across:

• In a segment on KJZZ (Phoenix's NPR station) this morning, Tony Ganzer reports on unraveling the heat advisories. Local heat advisories are relative to the time of year, and in the middle of an Arizona summer, the National Weather Service won't even consider issuing a heat advisory unless the temperature will go above 110 degrees. You can search the National Weather Service for real-time advisories and warnings in your own state.
• While extreme heat is dangerous, the human body actually possesses the capability to adapt to heat over time. NPR recently featured Phoenix in a news story about heat in urban settings. It turns out, Phoenix is considered the hottest city in the United States. Part of the article explains how people who spend more time exposed to heat are less susceptible to injury from heat than people who spend more time in air conditioned environments.

Amazingly, humans can adapt to this kind of blast-furnace heat – within limits. If you live in heat like this for just a few weeks, your body undergoes some remarkable changes.

New research shows one change involves chemicals called heat-shock proteins. They stop cells from committing suicide– their usual response to injury.

But if you live in a place where heat waves are uncommon – or spend a lot of time in air-conditioned rooms – scientists think your cells don't make as much heat-shock protein when you are exposed to high temperatures. That's one reason people in cities that aren't as hot as Phoenix can actually be at greater risk of heat stroke.

Dr. Sam Keim of the University of Arizona says chronic heat exposure touches off other changes in the body. Sweat increases, and the composition of sweat changes. It gets saltier.

Conserve salt and you prevent dehydration. That's important. In hot weather, your entire body acts like one big car radiator. Blood vessels near the skin open up to get rid of heat. Sweat cools the skin.

But if you sweat too much, your blood volume drops. Even a 1 percent drop forces the heart to pump faster and harder. That's bad news for people with heart disease.

And if your body's radiator can't shed heat fast enough, Keim says that's very bad news for the brain.

"People begin to have bizarre behavior," he says. "They're not thinking straight. So there's a direct effect of heat on brain function."

People edging into heat stroke often don't do what they should to protect themselves, such as drink water or get out of the sun. People with dementia and mental illness are at higher risk... [read more]

• The New York Times featured an article today titled "Sweatology," that discusses many of the same facts as the NPR piece. It was a really interesting article that explored the physiology of why we sweat, the anthropology of man's development of sweat glands, and clothing's and obesity's sociological relation to sweat.
• Part of the reason that major urban areas maintain higher temperatures is due to the "urban heat island" effect. As cities grow larger, more buildings are erected and more pavement is laid in order to provide the infrastructure for a growing population. Phoenix is one of the fastest growing metropolitan areas in the country too. So, as the sun beats down on these buildings and roadways all day, the structures are absorbing the heat, such that even once the sun has set for the day, heat is slowly being released into the atmosphere. This is why temperatures at night in Phoenix remain in the the triple digits!
  
  This past Saturday I went out for a training ride on my road bike. I explored an area that I had not been around before. At one point I was on a narrow 2 lane road (a mere 2 lanes is almost unheard of in Phoenix) with little traffic in the affluent area of Paradise Valley. The residential area came to an end at one point and I was surrounded by a golf course on both sides. I immediately felt a difference in temperatures, due to the large amount of green space that now surrounded me. The air was much cooler and even more humid - to an alarming extent. There must have been at least a 10 degree difference in temperature.
  
  I plan on writing some more about the heat island effect later this week because there is more to explore on this subject...

Anyway, I think we all have a pretty good idea about the science behind heat and the body's reaction to heat. We are often capable of withstanding more than we think we can. But again, BE PREPARED and BE SAFE. Let yourself be the judge of whether or not it is too hot for you to ride a bike, not some scientist quoted in a newspaper. If you don't feel up to the task, there is no need to push yourself too far.

Thanks to everyone who commented or emailed me about what you do to stay cool...besides riding a bike! Here's to you, and here's to the Velorution!