Outside the cook box a big blue plastic tub is filled with cold water for anyone whose temperature passes 103. Immersion in cold water is the quickest fix for heat illness. When a hot solid or liquid comes in contact with a cooler one, the hot one will become cooler and the cool one hotter. That’s conduction. Conduction explains why tropical shipwreck survivors can die of “warm water hypothermia.” As long as the sea is cooler than they are, they lose body heat to the water.
Conduction can also, of course, make a body hotter. Should you find yourself stranded in the desert, don’t rest directly on the ground—or lean against the Land Rover. Sand gets as hot as 130 degrees Fahrenheit; metal well hotter. Conduction helps explain why loose clothing keeps you cooler in the sun. A baggy shirt heats up, but because the cloth is not in contact with your skin, it does not—unlike a form-fitting t-shirt—conduct that heat to your body. (Loose clothes also let sweat evaporate more readily.)
Even better if the baggy shirt is white. Light-colored clothing reflects some of the sun’s radiation, so you get hit with less of it. Going shirtless in the sun makes a person hotter, not cooler. In Edward Adolph’s “‘nude’ men in the sun” study, subjects sitting on boxes wearing nothing but shoes, socks, and underwear suffered the equivalent of a ten-degree rise in air temperature. Adding to their discomfort, the control—a fully clothed man—was seated beside them. It’s not the heat, it’s the humiliation.
You can imagine how heat illness experts feel about sunbathers: people who willingly lie in direct sun, on hot sand, nearly nude. Small wonder it’s done in close proximity to the big blue tub known as the ocean. Just don’t get up off your towel and start lifting weights. Overworking a set of muscles puts you at risk for a potentially fatal condition called rhabdomyolysis. If the body can’t keep pace with a muscle’s extreme demand for fuel, eventually the muscle becomes ischemic. Heat exacerbates the scenario, because of the competing demand for plasma for making sweat. The cells of the oxygen-starved muscle tissue begin to break down, and their contents spill into the bloodstream. One of these breakdown components is potassium; high levels of it can cause cardiac arrest. Another, myoglobin, damages the kidneys—sometimes to the point of failure. Now you are a very buff and picturesque corpse.
Bodybuilding has been the number one pastime on bases in Afghanistan, where it is even hotter than in Venice Beach. The bodybuilding supplements soldiers take to bulk up more quickly exacerbate the risks. They often contain potentially dangerous compounds: stimulants that spur muscle contractility, thermogenic agents that rev the metabolism, and creatine, which accelerates dehydration. All of these increase the competition for the body’s limited blood supply. CHAMP runs an online resource, Operation Supplement Safety, that reviews the dangers of different products; however, with more than ninety thousand different supplements for sale on the Internet—and Amazon.com delivering to the major air bases—it’s a Sisyphean challenge. For those unfamiliar with the myth, Sisyphus was that Greek guy the gods punished by condemning him to roll an enormous boulder uphill forever, or until rhabdomyolysis set in. During 2011, there were 435 cases of exertional rhabdomyolysis among US service members.
Even simple protein supplements amplify the risks. Protein is deliquescent: It draws water from the body’s tissues into the bloodstream to help flush the protein breakdown products, which are tough on the excretory system. If you’re dying of thirst in the desert, drinking your urine won’t help you. The proteins and salts are by that point so concentrated that the body needs to pull fluid from the tissues to dilute them, which puts you back where you began, only worse, because now you are saddled with the memory of drinking your own murky, stinking pee.
Rhabdomyolysis also turns up at the other extreme of the bodybuild spectrum. Morbidly obese patients immobilized on their backs—say, for lengthy gastric bypass surgery—run the risk that their bodies will press down on the muscles of their backsides so hard that circulation is cut off. After four to six hours, the dying cells of the muscle tissue break open and leak, and when the patient finally moves, or is moved, the blood rushes back in and sweeps the breakdown products into the bloodstream in a sudden, overwhelming gush. Being pinned under rubble in an earthquake or in the wreckage of a car poses a similar risk. As does passing out drunk and lying without moving for six hours. This was explained to me by rhabdomyolysis researcher Darren Malinoski, an assistant chief of surgery at the Portland VA Medical Center. He added that rhabdomyolysis is one reason people roll over in their sleep. “The muscles are getting ischemic, and they make you move.”
“Look: Even your thighs are starting to flush,” says Dianna. All that overheated blood being shunted to my skin. “Do you want to try to keep going a full half hour with the pack on?”
Not even slightly. “I think I get it.”
Dianna asks the lads how they’re feeling. Josh’s fellow instructor, whose name is Dan Lessard, replies that he’s bored. Josh doesn’t hear the question because he’s got earbuds in. He removes one, and a tinny musical aggression leaks out. It’s Five Finger Death Punch, a metal band that from what I can tell uses synthesized machine-gun fire in place of a drummer.
Josh says he and Dan plan to do “a real workout” later in the day.
“Mary stopped after seven minutes with the pack on,” Dianna volunteers. Hey!
Josh defends me. “You don’t come out of the womb with a rucksack on. The first time I put it on, I hated my life.” He seems like a good person who has been handed a lot. His frivolity, his pep, whatever innocence we’re all born with, became something tougher in Iraq. War denatures people.
At 11:30, we’re released from the cook box. “And now you can go take out your friend,” says a lab tech named Kaitlin, referring to the probe. Earlier, in the midst of a conversation about idiosyncratic sweating patterns, Kaitlin raised both arms as though she’d just won Wimbledon and announced, “My right armpit sweats way more.” This we confirmed. Which bring us to the point of Dianna’s work: Genetic differences in thermoregulation—efficient/inefficient, left side/right side, you name it—are surprisingly large and well worth paying attention to, given our seemingly permanent posture of fighting extremism in the Middle East.
Dianna suggests heading to a nearby Walter Reed cafeteria to continue the conversation. Josh seconds. “Sustenance. Let’s get it.”