Hell-Bent by Benjamin Lorr Read Free Book Online

body temperature probes to hulking jocks. Given that intense heat is the sine qua non of my Bikram experience, she feels like the perfect person to talk with. Also given the logistics of rectal probes, I’m guessing she is pretty charismatic.
    When I talk with her, she is about to run fieldwork with firefighters, investigating the effectiveness of head-cooling helmets. The firefighters, dressed in full Vader-like protective gear, will run through training exercises designed to mimic real-life rescue operations while Dr. Yeargin attends to their physiology: capturing their core body temperature, heart rate, skin temperature, and sweat rate in action. The whole scene seems like the intersection of hard science and a romantic comedy, with the brainy, diminutiveDr. Yeargin on her tiptoes adjusting the placement of sensors while the fire-fighters lounge between training sessions, crack jokes, and prepare to rush back into danger.
    The data she collects will be analyzed backed at her lab. She hopes the results will be used to design better cooling systems for helmets—or perhaps to move away from head cooling completely.
    “I do a lot of work with children too,” she said. “And children are reasonable. When a child gets hot and verges on heat illness, they get grumpy and whiny and quit. Adults, on the other hand, tend to think they can push through anything.
    “One of the dangers of a head-cooling device might be that it encourages that mentality. It doesn’t help anyone if we have firefighters that think they are perfectly fine but are actually on the verge of collapse.”
    Understanding the mechanisms behind that collapse is what led Dr. Yeargin to study heat in the first place. In the summer of 2001, just as she was entering a master’s program in exercise science, she watched three consecutive heat stroke deaths ripple through the sporting world: one each at the high school, college, and pro level. The deaths were senseless and mysterious. One occurred at 88 degrees and 60 percent humidity, a typical Florida summer day. One occurred surrounded by coaches, trainers, and elite medical facilities. All involved athletes in prime physical condition who, after completing their workout for the day, simply fell into comas and died. The more she investigated, the more interested she became in the physiological mechanisms that triggered these deaths. She switched the focus of her master’s. When she was finished, she switched the focus of her career and began work on a Ph.D.
    From her office, Dr. Yeargin gives me a crash course in the physiology of exercise during extreme heat. “Your body is battling two sources of heat coming at it from two directions,” she explains. “First, inside the body, your muscles are producing heat through metabolism. Second, and more importantly, heat from the outside world is penetrating inward.” Combating these forces is absolutely essential to survival. The body has a critical core temperature just north of 105 degrees, after which the brain begins to shut down and organs start to fail.
    To exercise in heat is to create a series of dilemmas: the body must negotiate the urgent need for cooling with the desire to continue exercising.
    This begins with the body’s normal response to heat, shunting blood from the core to the skin. As blood cycles to the surface, it dissipates heat into the atmosphere and then cycles back to cool the entire system. During exertion, however, the muscles of the body require increases in blood to function. In response to the two separate needs, the body shunts blood in two directions: into the muscles to feed performance and out to the skin to cool. This fork, however, leaves a gap: the major organs of the body—especially the gut, liver, kidneys, and brain—can be underserved and undernourished.
    Compounding this rerouting is a massive relaxation of the vessels holding the circulating blood. Heat stimulates a reflex, dilating the size of the blood vessels. In