LIKE MOST FOOLPROOF ideas, this turned out to be a moronic oversimplification.

With only three months to go before the starting line, I scheduled a visit to the Boulder Center for Sports Medicine, a training facility that has coached Olympians. Prepared for the ugly truth, I was pleased to find I wasn't ruined after all. Sweet.

Forget runner's high. I chugged through the hills, barely passing adults carrying infants. Sorority girls in ill-fitting sweatpants waddled by me along Boulder Creek.

Three hours of performance tests revealed that my body was—drumroll—normal, with a respectable VO2 max of 54 on a scale of 30 to 70. The butt I gulped in the parking lot beforehand had little effect on the results. A cigarette's carbon monoxide, which robs red blood cells of space to transport oxygen, is quickly expelled under exertion, and half of the nicotine, a stimulant like amphetamines, had disappeared by the time I took the first treadmill torture test two hours later.

"Cigarettes probably haven't damaged your lungs," concluded Dr. Hunter Smith, the center's pulmonologist.

The most damning second opinion I could find hardly held my feet to the fire. "Your lung function is completely normal—actually at the upper end of normal, bordering on supernormal," said David P.L. Sachs, clinical associate professor of pulmonary and critical-care medicine at Stanford University Medical School. How could this be? "One person might notice airway irritation after just a couple cigarettes a day for a couple of years," he told me. "Another might smoke two packs a day and die at 95 without a wisp of shortness of breath. It depends on your genes."

Nonetheless, he assured me, I was playing Russian roulette with a two-barreled revolver. I'd been lucky so far. But I had a family history.

It was the sports lab's physiologist, Neal Henderson, who put the first dent in my motivation. He designed a heartbeat-by-heartbeat workout plan that centered on jogs so embarrassingly slow they could accurately be termed "dawdles."

"LSD, long slow distance, is what you need for the next three months," he said, prescribing a pulse rate of 138 to 156 sustained for one to three hours.

Forget runner's high. I chugged through the foothills, barely passing adults carrying infants. Chunky sorority girls in ill-fitting sweatpants waddled past me along Boulder Creek. Only once a week, when I ran fast enough to cough up great wads of phlegm, did my body reiterate what my mind knew: that I was probably sprinting toward the grave.

Quitting was a different story. Here, I was on my own. I quickly dropped to half a pack a day and whittled down from there. I removed all triggers—rearranged the deck furniture, switched from coffee to tea, avoided boozy barbecues. On road trips I ate sunflower seeds. When my resolve lapsed, I appeased the oral fixation by rolling smokes from the loose leaves of a green herb called damiana, which smells like dope and supposedly enhances your libido.

But my brain went haywire. Missing the neural lubricant that is nicotine, my synapses misfired. I stopped working for two weeks. After the initial depression it was kind of fun not knowing what I would say next. But I still couldn't give up those last precious cigs, the one or two I'd twist up each evening with rolling papers stolen from the homeopathic stuff. Perhaps because I'd never had to pay for my sins, I just couldn't shake them. By the time I left for Nunavut, I was running much faster but still running with the addiction.