BODY TEMPERATURE: 101 DEGREES Fahrenheit. Never mind that the air temperature is way too hot for hill climbing (92 degrees and rising). If you reach the top of the pass, you've won!
102 DEGREES. With each powerful downstroke of your pedals, your core temperature climbs a tiny fraction of a degree. You've entered the "fever of exercise" zone between 100 and 105 degrees—temperatures that trained athletes endure without harm.
103 DEGREES. Every nine seconds, each of your two million sweat glands squirts a drop of moisture through a pore, then recharges. Without the cooling mechanism of sweat, at the fierce pace you're riding, your body temperature would rise 0.9 degrees every minute and you'd reach heatstroke range within 12 minutes.
104 DEGREES. The road steepens. You stand on your pedals. Painful knots form in your biceps, calves, and abdominal muscles—heat cramps, believed to be the result of sweating out so much sodium. Though your heart pounds, it can't keep your veins and arteries filled to capacity; they've dilated to their maximum to bring hot blood from your overheated core to your sweat-cooled exterior. Lacking pressure, blood flow to your brain slackens. Your vision turns fuzzy.
105 DEGREES. You begin to hallucinate. The searing pain in your thighs suddenly eases. The finish line is just ahead. You know victory is yours but for some reason no one is there waiting. You veer off the road and tumble down an embankment. Everything goes black.
106 DEGREES. Lying unconscious, you suffer a heatstroke. Your cellular metabolic rate—how fast your cells turn fuels into energy—accelerates. Metabolism is now occurring more than 50 percent faster than at normal temperatures. Your body is literally cooking itself from within.
107 DEGREES. You vomit repeatedly, and your sphincter releases.
109 DEGREES. Seizures ripple through your muscles.
110 TO 113 DEGREES. Mitochondria and cellular proteins dissolve. Your heart and lungs start to hemorrhage. Blood coagulates in your veins. Heat damages your liver, kidneys, and brain and perforates your intestinal wall. Toxins emitted by spent digestive bacteria now escape into your bloodstream, perhaps triggering septic shock. Your heart stops.
THEY FIND YOU THAT EVENING, long after the race has ended. They can't locate a pulse, but your lifeless body is still warm to the touch.