It used to be that only mad dogs and Englishmen went out in the noonday sun. These days you might see anybody who owns a pair of Reeboks pounding around the track, down the street or through the park, working hard to live forever, paying no mind to the current heat wave.
So he looks a little pink, like a lover engulfed by a blush. It probably won't kill him -- not if he's in shape, accustomed to the climate and has been pumping fluids into that most efficient and adaptable of machines we call the human body.
If he's not in shape, has recently lived in Alaska or has refrained from water and such, he could be in trouble.
What precisely is happening to our determined jogger, this macho jock undeterred by Fahrenheit levels approaching 100?
This kind of heat has already killed well over 100 people in the Deep South and Western states, and it has finally found its way here. Yesterday it reached 98 degrees by 4 p.m., with a heat index of 102.
The jogger's blood is doing its best to rescue him from his brain's recklessness, in deciding he should exercise in weather like this. Blood is flowing out from the core of his body to the surface of his skin so the heat being generated within his body by his exertion can be dissipated into the air.
The red color -- the blush -- is evidence of the dilation of the capillaries on his skin; they are filling up with this large volume of blood.
Now, according to physicians and physiologists this is good. It is the body defending itself. And the body has an array of specific physiological defenses against heat besides this, things like heat-shock proteins which are being produced in the cells to protect them from heat stress.
As with all defenses, this one, the migration of the blood, has its limitations. In this case, the limitation relates to the supply. The blood engaged in getting rid of the heat at the surface of the body has to come from somewhere, right?
So where does it come from?
From vital organs like the kidneys, the brain, the heart. These need fresh blood, too, and don't like being deprived. Take the heart, for instance. With so much blood out on the periphery of the body, it has less to pump. So what happens?
Artin Shoukas, a physiologist and biomedical engineer at Johns Hopkins Medical School, explains the sequence: "Your blood pressure decreases. You start to feel faint. And, usually because you are standing, you don't have enough blood going to the brain. So you faint."
If the blood flow to the heart drops enough, the heart can fail. You can die.
This doesn't happen all that often. "The human organism, says Dr. Robert Fitzgerald, a respiratory physiologist at Hopkins, "really knows how to manage a precipitous fall in blood pressure."
But athletes can run extra risk.
With the International Lacrosse World Championship going on this week at Hopkins' Homeland campus, "I thought that these guys better watch themselves out there," said Fitzgerald. "When you exercise you give off a lot of heat. They're trained at reasonable ambient temperatures, but these days temperatures are not reasonable. What you got is internally generated heat and ambient heat."
Which is to say, it is increasingly difficult to lose heat in an atmosphere that is also overheated. And it is increasingly difficult to evaporate sweat -- another of the body's cooling mechanisms -- in an atmosphere saturated with humidity.
There are other troubles when it comes to exertions made in high temperatures.
"When you start exercising, the blood flow is diverted to working muscles in the legs and limbs, and your heart has to start #F pumping more blood to those muscles," Shoukas says. "They need oxygen and nutrients."
Trouble is, your blood flow is already decreased because of that flow of blood away from the heart to the surface of the skin.
"In these circumstances you often can't get enough blood to the muscles, so the muscles start to fatigue," he says. "You can cramp up."
Worse, you can put too great a strain on your heart.
Sweating up a storm
Sweating is the most efficient way of cooling the body, short of diving into a mountain lake or going into an air-conditioned bar. Sweat cools by carrying heat away through evaporation. Human beings are well-equipped for this: Each one of us has 2 million to 4 million sweat glands. Taken together, they weigh about 3 ounces. Women have more than men.
At the lacrosse tournament on University Parkway, there's plenty of sweat out on the field. And, of course, there are plenty of fluids for the players to drink to replace body fluids. For the fans there are drinks, and something else: Misting tents have been set up on the adjacent baseball field.
Step in, walk through a fine spray and you come out exceedingly damp. It's a great way to cool down fast, if you don't mind soggy clothes.