In his new book, To The Last Breath, physicist Francis Slakey recounts the myriad of physical and mental challenges in summiting the world’s highest peak. The following is an excerpt from To The Last Breath, full of vivid detail:

I take my first step down the mountain and immediately feel depleted. Adrenaline is a direction-sensitive stimulant. My body has been producing gallons of it since I set out for the summit at midnight, but the moment I turned around to go back down the spigot went dry. I have felt this on every climb I have ever done and other climbers tell me they experience the same thing: adrenaline on the way up, an empty tank on the way down.

These are the moments when I have my greatest focus. It’s not that my mind is sharp; at this altitude, with this level of fatigue, I know that my mind is as thick as timber. And it’s not that I’m broadly aware of my circumstances.

In fact, now, at this moment, my world has become astonishingly small. It no longer consists of friends and family.  My hometown, the smell of coffee, the push and hustle of my job, the last book I read—all of that is distant and forgotten. 

The only thing that exists in my life right now is the square foot of snow directly in front of me where I will plant my next step. I can sense that spot with absolute clarity. I can see the bend of the snow, feel the weight of the falling flakes, sense the flakes settle on the ridge creating a new contour. The shadows and folds of a small patch of snow and rock are my entire world now.

I guide my foot to the spot I’ve been staring at and the metal claws of my crampon punch through the snow, gripping and taking my weight as I lean forward sinking deep into fresh powder. I take in three breaths before I’m ready for another step. I pull my boot out of the foot-deep hole of snow and plod forward. This descent is happening in slow motion, like walking through a vat of molasses.

My speed is limited by the intense fatigue and the layers of clothes I’m wearing to weather the twenty-below-zero temperature. I’m encased in a down suit, hands sealed in thick gloves, my face layered in a mask and goggles. Two days from now, when I’m back in Base Camp, I will discover that there was a small gap in all that wrapping. A square of flesh on my cheek, no bigger than a postage stamp, was exposed to the subzero chill. The result is a patch of thick blackened skin, crisped like a burnt marshmallow. It takes months for the skin to return but it forever remains sensitive to the cold.

On the final challenge of reaching the death zone:

As a climber goes up even higher in altitude, into the so-called death zone, the dangerously thin air above 26,000 feet, there is so little oxygen available that the body makes a desperate decision: it cuts off the digestive system. The body can no longer afford to direct oxygen to the stomach to help digest food because that would divert what precious little oxygen is available away from the brain. The body will retch back up anything the climber tries to eat, even if it’s as small as an M&M.

The consequence of shutting down the digestive system is, of course, that the body can no longer take in any calories. Lacking an external fuel source, the body has no choice but to turn on itself.  It now fuels itself by burning its own muscle—the very muscle needed to climb the mountain—at a rate of about two pounds per hour.

The climber’s body is now in total collapse. The respiratory system is working way beyond its tolerance at roughly four times above normal; the circulatory system is pumping at only 30 percent capacity; the digestive system has completely shut down; and the muscular system is eating away at itself. In short, the body is dying. Rapidly. 

Read the entire excerpt here. I’ve placed To The Last Breath in my reading queue.

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(hat tip: @travelreads)